Publications by authors named "Michael V Kolomiets"

33 Publications

Raman Spectroscopy as a Robust New Tool for Rapid and Accurate Evaluation of Drought Tolerance Levels in Both Genetically Diverse and Near-Isogenic Maize Lines.

Front Plant Sci 2021 12;12:621711. Epub 2021 Jul 12.

Electrical and Computer Engineering Department, Texas A&M University, College Station, TX, United States.

Improving drought tolerance of crops has become crucial due to the current scenario of rapid climate change. In particular, development of new maize germplasm with increased drought tolerance is viewed as a major breeding goal to ensure sustainable food and feed production. Therefore, accurate rapid phenotyping techniques for selection of superior maize genotypes are required. The objectives of this study were to determine whether Raman microscopy technique can be applied for accurate assessment of drought-tolerance levels in both genetically diverse and near-isogenic maize lines that differ in their levels of drought-tolerance. Carotenoid degradation is known to be a direct stress response initiated by reactive oxygen species during osmotic stress such as drought. Using Raman mapping, we observed real-time changes in the rate of carotenoid degradation in chloroplasts that was dependent on the strength of osmotic stress. In addition, we showed that the rate of carotenoid degradation as measured by Raman spectroscopy correlates directly with drought tolerance levels of diverse maize genotypes. We conclude that Raman technique is a robust, biochemically selective and non-invasive phenotyping technique that accurately distinguishes drought tolerance levels in both genetically diverse and near-isogenic maize genotypes. We conclude that this technique can be further developed to render it suitable for field-based early assessment of breeding materials with superior drought-tolerance traits.
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http://dx.doi.org/10.3389/fpls.2021.621711DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8311160PMC
July 2021

induces maize-derived ethylene to promote virulence by engaging fungal G-protein signaling.

Mol Plant Microbe Interact 2021 Jun 24. Epub 2021 Jun 24.

Texas A&M University System, 2655, Plant Pathology and Microbiology, College Station, Texas, United States;

Seed maceration and contamination with mycotoxin fumonisin inflicted by is major disease of concern for maize producers world-wide. Meta-analyses of QTL for ear rot resistance uncovered several ethylene (ET) biosynthesis and signaling genes within them, implicating ET in maize interactions with . We tested this hypothesis using maize knock-out mutants of the 1-aminocyclopropane-1-carboxylate (ACC) synthases, and . Infected wild-type seed emitted five-fold higher ET levels compared to controls, whereas ET was abolished in the and single and double mutants. The mutants supported reduced fungal biomass, conidia and fumonisin content. Normal susceptibility was restored in the mutant with exogenous treatment of ET precursor, ACC. Subsequently, we showed that fungal G-protein signaling is required for virulence via induction of maize-produced ET. G subunit and two regulators of G-protein signaling mutants displayed reduced seed colonization and decreased ET levels. These defects were rescued by exogenous application of ACC. We concluded that pathogen-induced ET facilitates colonization of seed, and in turn host ET production is manipulated via G-protein signaling of to facilitate pathogenesis.
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http://dx.doi.org/10.1094/MPMI-09-20-0250-RDOI Listing
June 2021

Genome-Wide Characterization of Jasmonates Signaling Components Reveals the Essential Role of ZmCOI1a-ZmJAZ15 Action Module in Regulating Maize Immunity to Gibberella Stalk Rot.

Int J Mol Sci 2021 Jan 16;22(2). Epub 2021 Jan 16.

State Key Laboratory for Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanjing 210095, China.

Gibberella stalk rot (GSR) by causes significant losses of maize production worldwide. Jasmonates (JAs) have been broadly known in regulating defense against pathogens through the homeostasis of active JAs and COI-JAZ-MYC function module. However, the functions of different molecular species of JAs and COI-JAZ-MYC module in maize interactions with and regulation of diverse metabolites remain unknown. In this study, we found that exogenous application of MeJA strongly enhanced resistance to GSR. RNA-seq analysis showed that MeJA activated multiple genes in JA pathways, which prompted us to perform a genome-wide screening of key JA signaling components in maize. Yeast Two-Hybrid, Split-Luciferase, and Pull-down assays revealed that the JA functional and structural mimic coronatine (COR) functions as an essential ligand to trigger the interaction between ZmCOIa and ZmJAZ15. By deploying CRISPR-cas9 knockout and insertional mutants, we demonstrated that mutant is more resistant, whereas mutant is more susceptible to GSR. Moreover, JA-deficient mutant displayed enhanced resistance to GSR compared to wild type. Together, these results provide strong evidence that plays a pivotal role, whereas and endogenous JA itself might function as susceptibility factors, in maize immunity to GSR.
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http://dx.doi.org/10.3390/ijms22020870DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7830991PMC
January 2021

Oxylipins are implicated as communication signals in tomato-root-knot nematode (Meloidogyne javanica) interaction.

Sci Rep 2021 01 11;11(1):326. Epub 2021 Jan 11.

Department of Entomology, Nematology and Chemistry Units, Agricultural Research Organization (ARO), The Volcani Center, P.O. Box 15159, 50250, Rishon LeZion, Bet Dagan, Israel.

Throughout infection, plant-parasitic nematodes activate a complex host defense response that will regulate their development and aggressiveness. Oxylipins-lipophilic signaling molecules-are part of this complex, performing a fundamental role in regulating plant development and immunity. At the same time, the sedentary root-knot nematode Meloidogyne spp. secretes numerous effectors that play key roles during invasion and migration, supporting construction and maintenance of nematodes' feeding sites. Herein, comprehensive oxylipin profiling of tomato roots, performed using LC-MS/MS, indicated strong and early responses of many oxylipins following root-knot nematode infection. To identify genes that might respond to the lipidomic defense pathway mediated through oxylipins, RNA-Seq was performed by exposing Meloidogyne javanica second-stage juveniles to tomato protoplasts and the oxylipin 9-HOT, one of the early-induced oxylipins in tomato roots upon nematode infection. A total of 7512 differentially expressed genes were identified. To target putative effectors, we sought differentially expressed genes carrying a predicted secretion signal peptide. Among these, several were homologous with known effectors in other nematode species; other unknown, potentially secreted proteins may have a role as root-knot nematode effectors that are induced by plant lipid signals. These include effectors associated with distortion of the plant immune response or manipulating signal transduction mediated by lipid signals. Other effectors are implicated in cell wall degradation or ROS detoxification at the plant-nematode interface. Being an integral part of the plant's defense response, oxylipins might be placed as important signaling molecules underlying nematode parasitism.
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http://dx.doi.org/10.1038/s41598-020-79432-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7801703PMC
January 2021

Plant hairy roots enable high throughput identification of antimicrobials against Candidatus Liberibacter spp.

Nat Commun 2020 11 16;11(1):5802. Epub 2020 Nov 16.

Texas A&M AgriLife Research and Extension Center, Weslaco, TX, USA.

A major bottleneck in identifying therapies to control citrus greening and other devastating plant diseases caused by fastidious pathogens is our inability to culture the pathogens in defined media or axenic cultures. As such, conventional approaches for antimicrobial evaluation (genetic or chemical) rely on time-consuming, low-throughput and inherently variable whole-plant assays. Here, we report that plant hairy roots support the growth of fastidious pathogens like Candidatus Liberibacter spp., the presumptive causal agents of citrus greening, potato zebra chip and tomato vein greening diseases. Importantly, we leverage the microbial hairy roots for rapid, reproducible efficacy screening of multiple therapies. We identify six antimicrobial peptides, two plant immune regulators and eight chemicals which inhibit Candidatus Liberibacter spp. in plant tissues. The antimicrobials, either singly or in combination, can be used as near- and long-term therapies to control citrus greening, potato zebra chip and tomato vein greening diseases.
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http://dx.doi.org/10.1038/s41467-020-19631-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7669877PMC
November 2020

colonization of maize roots triggers rapid accumulation of 12-oxophytodienoate and two ᵧ-ketols in leaves as priming agents of induced systemic resistance.

Plant Signal Behav 2020 09 11;15(9):1792187. Epub 2020 Jul 11.

Department of Plant Pathology and Microbiology, Texas A&M University , College Station, TX USA.

Two oxylipins 12-OPDA (12-Oxo-10(),15()-phytodienoic acid) and an ᵧ-ketol, 9,10-KODA (10-oxo-9-hydroxy-12(), 15()-octadecadienoic acid) were recently identified as important long-distance-induced systemic resistance (ISR) signals in -treated maize. On the other hand, jasmonic acid (JA), long believed to be a major signal of ISR, was not involved, as the JA-deficient mutant, , retained the capacity for -triggered ISR. In order to further understand the biochemical basis for ISR priming in maize leaves, diverse oxylipins and phytohormones in the leaves of wild-type maize or ISR-deficient mutants treated with were quantified. This analysis revealed that 12-OPDA and two novel ᵧ-ketols, 9,12-KOMA (12-Oxo-9-hydroxy-10()-octadecenoic acid) and 9,12-KODA (12-Oxo-9-hydroxy-10(),15()-octadecadienoic acid), accumulated at high levels in ISR-positive plants. In support of the notion that 12-OPDA serves as a priming agent for ISR in addition to being a xylem-mobile signal, leaf pretreatment with this JA precursor resulted in increased resistance to . Furthermore, the injection of 9,12-KODA or 9,12-KOMA in wild-type plants enhanced resistance against infection, suggesting that they play roles in ISR priming.
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http://dx.doi.org/10.1080/15592324.2020.1792187DOI Listing
September 2020

Maize defense elicitor, 12-oxo-phytodienoic acid, prolongs aphid salivation.

Commun Integr Biol 2020 13;13(1):63-66. Epub 2020 May 13.

Department of Entomology, University of Nebraska-Lincoln, Lincoln, NE, USA.

12-Oxo-phytodienoic acid (OPDA), an intermediate in the jasmonic acid (JA) biosynthesis pathway, regulates diverse signaling functions in plants, including enhanced resistance to insect pests. We previously demonstrated that OPDA promoted enhanced callose accumulation and heightened resistance to corn leaf aphid (CLA; ), a phloem sap-sucking insect pest of maize (). In this study, we used the electrical penetration graph (EPG) technique to monitor and quantify the different CLA feeding patterns on the maize JA-deficient () plants. CLA feeding behavior was unaffected on B73, control plants (- OPDA), and plants that were pretreated with OPDA (+ OPDA). However, exogenous application of OPDA on plants prolonged aphid salivation, a hallmark of aphids' ability to suppress the plant defense responses. Collectively, our results indicate that CLA utilizes its salivary secretions to suppress or unplug the OPDA-mediated sieve element occlusions in maize.
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http://dx.doi.org/10.1080/19420889.2020.1763562DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7238879PMC
May 2020

Relative contribution of LOX10, green leaf volatiles and JA to wound-induced local and systemic oxylipin and hormone signature in Zea mays (maize).

Phytochemistry 2020 Jun 13;174:112334. Epub 2020 Mar 13.

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX, 77843, USA. Electronic address:

Green leaf volatiles (GLVs) and jasmonates (JAs) are the best-characterized groups of fatty acid-derived oxylipin signals that regulate wound-associated defenses. Beyond these two major groups of defense signals, plants produce an array of oxylipins in response to wounding, which possess potent signaling and/or insecticidal activities. In this study, we assessed the relative contribution of JAs and GLVs to wound-induced systemic signaling and the associated regulation of oxylipins in local and systemic tissues of maize (Zea mays). For this, we utilized GLV- and JA-deficient mutants, lox10 single and opr7opr8 double mutants, respectively, and profiled oxylipins in untreated leaves and roots, and in locally wounded and systemic leaves. In contrast to the studies in dicots, no systemic induction of JAs was observed in maize. Instead, a JA precursor, 12-OPDA, as well as ketols and C oxo-acids derived from 13-lipoxygenases (LOXs), were preferentially induced in both locally wounded and systemic unwounded leaves. Several 9-LOX-derived oxylipins (9-oxylipins) including hydroxides and ketones were also significantly induced locally. JA and JA-isoleucine (JA-Ile) were rapidly induced within 0.5 h, and were followed by a second increase in local tissue 4 h after wounding. GLV-deficient lox10 mutants displayed reduced levels of most 13-oxylipins, and elevated levels of several 9-oxylipins and the a-dioxygenase (DOX) product, 2-HOD. lox10 mutants were completely devoid of C volatiles and their C counterparts, and greatly decreased in C volatiles and their C oxo-acid counterparts. Thus, in addition to being the sole LOX isoform providing substrate for GLV synthesis, LOX10 is a major 13-LOX that provides substrate to several LOX branches that produce an array of 13-oxylipin products, including C volatiles. Interestingly, the rapid JA and JA-Ile increase at 0.5-2 h post-wounding was only moderately affected by the LOX10 mutation, while significantly reduced levels were observed at 4 h post-wounding. Combined with the previous findings that GLVs activate JA biosynthesis, these results suggest that both LOX10-derived substrates and/or GLVs are involved in the large second phase of JA synthesis proximal to the wound. Analyses of opr7opr8 mutants revealed that wound-induced oxylipin responses were positively regulated by JA signaling. The local and systemic accumulation of SA was not altered in the two mutants. Collectively, our results identified a subset of oxylipins strongly induced in wounded and systemic leaves, but their impact on insect defenses remain elusive. The lack of systemic induction of JAs points to substantial difference between systemic wound responses in studied dicots and maize. Our results show that GLV-deficiency and reduced JA in lox10 mutants had a greater impact on wound-induced local and systemic tissue oxylipin responses compared to the solely JA-deficient opr7opr8 double mutants. This suggests that GLVs or other LOX10-derived products heavily contribute to overall basal and wound-induced oxylipin responses. The specific roles of the GLV- and/or JA-dependent oxylipins in wound responses and defense remain to be further investigated by a combination of multiple orders of oxylipin-deficient mutants.
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http://dx.doi.org/10.1016/j.phytochem.2020.112334DOI Listing
June 2020

Green leaf volatiles and jasmonic acid enhance susceptibility to anthracnose diseases caused by Colletotrichum graminicola in maize.

Mol Plant Pathol 2020 05 27;21(5):702-715. Epub 2020 Feb 27.

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX, USA.

Colletotrichum graminicola is a hemibiotrophic fungus that causes anthracnose leaf blight (ALB) and anthracnose stalk rot (ASR) in maize. Despite substantial economic losses caused by these diseases, the defence mechanisms against this pathogen remain poorly understood. Several hormones are suggested to aid in defence against C. graminicola, such as jasmonic acid (JA) and salicylic acid (SA), but supporting genetic evidence was not reported. Green leaf volatiles (GLVs) are a group of well-characterized volatiles that induce JA biosynthesis in maize and are known to function in defence against necrotrophic pathogens. Information regarding the role of GLVs and JA in interactions with (hemi)biotrophic pathogens remains limited. To functionally elucidate GLVs and JA in defence against a hemibiotrophic pathogen, we tested GLV- and JA-deficient mutants, lox10 and opr7 opr8, respectively, for resistance to ASR and ALB and profiled jasmonates and SA in their stalks and leaves throughout infection. Both mutants were resistant and generally displayed elevated levels of SA and low amounts of jasmonates, especially at early stages of infection. Pretreatment with GLVs restored susceptibility of lox10 mutants, but not opr7 opr8 mutants, which coincided with complete rescue of JA levels. Exogenous methyl jasmonate restored susceptibility in both mutants when applied before inoculation, whereas methyl salicylate did not induce further resistance in either of the mutants, but did induce mutant-like resistance in the wild type. Collectively, this study reveals that GLVs and JA contribute to maize susceptibility to C. graminicola due to suppression of SA-related defences.
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http://dx.doi.org/10.1111/mpp.12924DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7170777PMC
May 2020

Oxylipins Other Than Jasmonic Acid Are Xylem-Resident Signals Regulating Systemic Resistance Induced by in Maize.

Plant Cell 2020 01 4;32(1):166-185. Epub 2019 Nov 4.

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843

Multiple long-distance signals have been identified for pathogen-induced systemic acquired resistance, but mobile signals for symbiont-induced systemic resistance (ISR) are less well understood. We used ISR-positive and -negative mutants of maize () and the beneficial fungus and identified 12-oxo-phytodienoic acid (12-OPDA) and α-ketol of octadecadienoic acid (KODA) as important ISR signals. We show that a maize 13-lipoxygenase mutant, , colonized by the wild-type (TvWT) lacked ISR response against but instead displayed induced systemic susceptibility. Oxylipin profiling of xylem sap from -treated plants revealed that 12-OPDA and KODA levels correlated with ISR. Transfusing sap supplemented with 12-OPDA or KODA increased receiver plant resistance in a dose-dependent manner, with 12-OPDA restoring ISR of plants treated with TvWT or , a mutant unable to induce ISR. Unexpectedly, jasmonic acid (JA) was not involved, as the JA-deficient mutant plants retained the capacity for -induced ISR. Transcriptome analysis of TvWT-treated maize B73 revealed upregulation of 12-OPDA biosynthesis and OPDA-responsive genes but downregulation of JA biosynthesis and JA response genes. We propose a model that differential regulation of 12-OPDA and JA in response to colonization results in ISR induction.
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http://dx.doi.org/10.1105/tpc.19.00487DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6961617PMC
January 2020

Rosette core fungal resistance in Arabidopsis thaliana.

Planta 2019 Dec 16;250(6):1941-1953. Epub 2019 Sep 16.

BioSciences Department, Rice University, Houston, TX, 77005, USA.

Main Conclusion: Unlike rosette leaves, the mature Arabidopsis rosette core can display full resistance to Botrytis cinerea revealing the importance for spatial and developmental aspects of plant fungal resistance. Arabidopsis thaliana is a model host to investigate plant defense against fungi. However, many of the reports investigating Arabidopsis fungal defense against the necrotrophic fungus, Botrytis cinerea, utilize rosette leaves as host tissue. Here we report organ-dependent differences in B. cinerea resistance of Arabidopsis. Although wild-type Arabidopsis rosette leaves mount a jasmonate-dependent defense that slows fungal growth, this defense is incapable of resisting fungal devastation. In contrast, as the fungus spreads through infected leaf petioles towards the plant center, or rosette core, there is a jasmonate- and age-dependent fungal penetration blockage into the rosette core. We report evidence for induced and preformed resistance in the rosette core, as direct rosette core inoculation can also result in resistance, but at a lower penetrance relative to infections that approach the core from infected leaf petioles. The Arabidopsis rosette core displays a distinct transcriptome relative to other plant organs, and BLADE ON PETIOLE (BOP) transcripts are abundant in the rosette core. The BOP genes, with known roles in abscission zone formation, are required for full Arabidopsis rosette core B. cinerea resistance, suggesting a possible role for BOP-dependent modifications that may help to restrict fungal susceptibility of the rosette core. Finally, we demonstrate that cabbage and cauliflower, common Brassicaceae crops, also display leaf susceptibility and rosette core resistance to B. cinerea that can involve leaf abscission. Thus, spatial and developmental aspects of plant host resistance play critical roles in resistance to necrotrophic fungal pathogens and are important to our understanding of plant defense mechanisms.
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http://dx.doi.org/10.1007/s00425-019-03273-5DOI Listing
December 2019

12-Oxo-Phytodienoic Acid Acts as a Regulator of Maize Defense against Corn Leaf Aphid.

Plant Physiol 2019 04 14;179(4):1402-1415. Epub 2019 Jan 14.

Department of Entomology, University of Nebraska, Lincoln, Nebraska 68583

The corn leaf aphid (CLA; ) is a phloem sap-sucking insect that attacks many cereal crops, including maize (). We previously showed that the maize inbred line Mp708, which was developed by classical plant breeding, provides enhanced resistance to CLA. Here, using electrophysiological monitoring of aphid feeding behavior, we demonstrate that Mp708 provides phloem-mediated resistance to CLA. Furthermore, feeding by CLA on Mp708 plants enhanced callose deposition, a potential defense mechanism utilized by plants to limit aphid feeding and subsequent colonization. In maize, benzoxazinoids (BX) or BX-derived metabolites contribute to enhanced callose deposition by providing heightened resistance to CLA. However, BX and BX-derived metabolites were not significantly altered in CLA-infested Mp708 plants, indicating BX-independent defense against CLA. Evidence presented here suggests that the constitutively higher levels of 12-oxo-phytodienoic acid (OPDA) in Mp708 plants contributed to enhanced callose accumulation and heightened CLA resistance. OPDA enhanced the expression of ethylene biosynthesis and receptor genes, and the synergistic interactions of OPDA and CLA feeding significantly induced the expression of the transcripts encoding Maize insect resistance1-Cysteine Protease, a key defensive protein against insect pests, in Mp708 plants. Furthermore, exogenous application of OPDA on maize jasmonic acid-deficient plants caused enhanced callose accumulation and heightened resistance to CLA, suggesting that the OPDA-mediated resistance to CLA is independent of the jasmonic acid pathway. We further demonstrate that the signaling function of OPDA, rather than a direct toxic effect, contributes to enhanced CLA resistance in Mp708.
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http://dx.doi.org/10.1104/pp.18.01472DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6446797PMC
April 2019

Ethylene signaling regulates natural variation in the abundance of antifungal acetylated diferuloylsucroses and Fusarium graminearum resistance in maize seedling roots.

New Phytol 2019 03 2;221(4):2096-2111. Epub 2018 Nov 2.

Boyce Thompson Institute, 533 Tower Road, Ithaca, NY, 14853, USA.

The production and regulation of defensive specialized metabolites play a central role in pathogen resistance in maize (Zea mays) and other plants. Therefore, identification of genes involved in plant specialized metabolism can contribute to improved disease resistance. We used comparative metabolomics to identify previously unknown antifungal metabolites in maize seedling roots, and investigated the genetic and physiological mechanisms underlying their natural variation using quantitative trait locus mapping and comparative transcriptomics approaches. Two maize metabolites, smilaside A (3,6-diferuloyl-3',6'-diacetylsucrose) and smiglaside C (3,6-diferuloyl-2',3',6'-triacetylsucrose), were identified that could contribute to maize resistance against Fusarium graminearum and other fungal pathogens. Elevated expression of an ethylene signaling gene, ETHYLENE INSENSITIVE 2 (ZmEIN2), co-segregated with a decreased smilaside A : smiglaside C ratio. Pharmacological and genetic manipulation of ethylene availability and sensitivity in vivo indicated that, whereas ethylene was required for the production of both metabolites, the smilaside A : smiglaside C ratio was negatively regulated by ethylene sensitivity. This ratio, rather than the absolute abundance of these two metabolites, was important for maize seedling root defense against F. graminearum. Ethylene signaling regulates the relative abundance of the two F. graminearum-resistance-related metabolites and affects resistance against F. graminearum in maize seedling roots.
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http://dx.doi.org/10.1111/nph.15520DOI Listing
March 2019

Nonsensical choices? Fall armyworm moths choose seemingly best or worst hosts for their larvae, but neonate larvae make their own choices.

PLoS One 2018 24;13(5):e0197628. Epub 2018 May 24.

Department of Entomology, Texas A&M University, College Station, TX, United States of America.

Selecting optimal host plants is critical for herbivorous insects, such as fall armyworm (Spodoptera frugiperda), an important maize pest in the Americas and Africa. Fall armyworm larvae are presumed to have limited mobility, hence female moths are presumed to be largely responsible for selecting hosts. We addressed host selection by fall armyworm moths and neonate and older (3rd-instar) larvae, as mediated by resistance and herbivory in maize plants. Thus, we compared discrimination among three maize cultivars with varying degrees of resistance to fall armyworm, and between plants subjected or not to two types of herbivory. The cultivars were: (i) susceptible, and deficient in jasmonic acid (JA) production and green leaf volatiles (GLV) emissions (inbred line B73-lox10); (ii) modestly resistant (B73), and; (iii) highly resistant (Mp708). The herbivory types were: (i) ongoing (= fall armyworm larvae present), and; (ii) future (= fall armyworm eggs present). In choice tests, moths laid more eggs on the highly resistant cultivar, and least on the susceptible cultivar, though on those cultivars larvae performed poorest and best, respectively. In the context of herbivory, moths laid more eggs: (i) on plants subject to versus free of future herbivory, regardless of whether plants were deficient or not in JA and GLV production; (ii) on plants subject versus free of ongoing herbivory, and; (iii) on plants not deficient in compared to deficient in JA and GLV production. Neonate larvae dispersed aerially from host plants (i.e. ballooned), and most larvae colonized the modestly resistant cultivar, and fewest the highly resistant cultivar, suggesting quasi-directional, directed aerial descent. Finally, dispersing older larvae did not discriminate among the three maize cultivars, nor between maize plants and (plastic) model maize plants, suggesting random, visually-oriented dispersal. Our results were used to assemble a model of host selection by fall armyworm moths and larvae, including recommendations for future research.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0197628PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5967860PMC
December 2018

Oxylipins from both pathogen and host antagonize jasmonic acid-mediated defence via the 9-lipoxygenase pathway in Fusarium verticillioides infection of maize.

Mol Plant Pathol 2018 09 17;19(9):2162-2176. Epub 2018 Jul 17.

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843-2132, USA.

Oxylipins are a newly emerging group of signals that serve defence roles or promote virulence. To identify specific host and fungal genes and oxylipins governing the interactions between maize and Fusarium verticillioides, maize wild-type and lipoxygenase3 (lox3) mutant were inoculated with either F. verticillioides wild-type or linoleate-diol-synthase 1-deleted mutant (ΔFvlds1D). The results showed that lox3 mutants were more resistant to F. verticillioides. The reduced colonization on lox3 was associated with reduced fumonisin production and with a stronger and earlier induction of ZmLOX4, ZmLOX5 and ZmLOX12. In addition to the reported defence function of ZmLOX12, we showed that lox4 and lox5 mutants were more susceptible to F. verticillioides and possessed decreased jasmonate levels during infection, suggesting that these genes are essential for jasmonic acid (JA)-mediated defence. Oxylipin profiling revealed a dramatic reduction in fungal linoleate diol synthase 1 (LDS1)-derived oxylipins, especially 8-HpODE (8-hydroperoxyoctadecenoic acid), in infected lox3 kernels, indicating the importance of this molecule in virulence. Collectively, we make the following conclusions: (1) LOX3 is a major susceptibility factor induced by fungal LDS1-derived oxylipins to suppress JA-stimulating 9-LOXs; (2) LOX3-mediated signalling promotes the biosynthesis of virulence-promoting oxylipins in the fungus; and (3) both fungal LDS1- and host LOX3-produced oxylipins are essential for the normal infection and colonization processes of maize seed by F. verticillioides.
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http://dx.doi.org/10.1111/mpp.12690DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6638020PMC
September 2018

Characterization of the maize lipoxygenase gene family in relation to aflatoxin accumulation resistance.

PLoS One 2017 17;12(7):e0181265. Epub 2017 Jul 17.

USDA-ARS Corn Host Plant Resistance Research Unit, Starkville, MS, United States of America.

Maize (Zea mays L.) is a globally important staple food crop prone to contamination by aflatoxin, a carcinogenic secondary metabolite produced by the fungus Aspergillus flavus. An efficient approach to reduce accumulation of aflatoxin is the development of germplasm resistant to colonization and toxin production by A. flavus. Lipoxygenases (LOXs) are a group of non-heme iron containing dioxygenase enzymes that catalyze oxygenation of polyunsaturated fatty acids (PUFAs). LOX derived oxylipins play critical roles in plant defense against pathogens including A. flavus. The objectives of this study were to summarize sequence diversity and expression patterns for all LOX genes in the maize genome, and map their effect on aflatoxin accumulation via linkage and association mapping. In total, 13 LOX genes were identified, characterized, and mapped. The sequence of one gene, ZmLOX10, is reported from 5 inbred lines. Genes ZmLOX1/2, 5, 8, 9, 10 and 12 (GRMZM2G156861, or V4 numbers ZM00001D042541 and Zm00001D042540, GRMZM2G102760, GRMZM2G104843, GRMZM2G017616, GRMZM2G015419, and GRMZM2G106748, respectively) fell under previously published QTL in one or more mapping populations and are linked to a measurable reduction of aflatoxin in maize grains. Association mapping results found 28 of the 726 SNPs tested were associated with reduced aflatoxin levels at p ≤ 9.71 x 10-4 according to association statistics. These fell within or near nine of the ZmLOX genes. This work confirms the importance of some lipoxygenases for resistance to aflatoxin accumulation and may be used to direct future genetic selection in maize.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0181265PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5513560PMC
October 2017

Reply to Dong and Zhao: Plant stress via Raman spectroscopy.

Proc Natl Acad Sci U S A 2017 07 27;114(28):E5488-E5490. Epub 2017 Jun 27.

Institute for Quantum Science and Engineering, Texas A&M University, College Station, TX 77843;

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http://dx.doi.org/10.1073/pnas.1707722114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5514768PMC
July 2017

Seed-Derived Ethylene Facilitates Colonization but Not Aflatoxin Production by in Maize.

Front Plant Sci 2017 28;8:415. Epub 2017 Mar 28.

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX, USA.

Ethylene (ET) emitted by plant tissues has been broadly reported to play important roles in plant development, response to environmental stresses and defense against certain pathogens. Recent evidence obtained from using fungal cultures exposed to ET suggested that exogenous ET may regulate the production of aflatoxin by . However, the function of endogenous, seed-derived ET has not been explored. In this study, we found that the maize lipoxygenase mutant, previously reported to be susceptible to spp., emitted greater levels of ET upon infection, suggesting the potential involvement of endogenous ET in the susceptibility of maize to . Supporting this idea, both colonization and conidiation of were reduced in wild-type (WT) kernels treated with AgNO, an ET synthesis inhibitor. There was no ET emission from non-viable kernels colonized by , suggesting that living seed but not the fungus itself was the primary source of ET released upon infection with . The kernels of and , two ET biosynthetic mutants carrying transposons in the ACC synthase genes, and , respectively, displayed enhanced seed colonization and conidiation, but not the levels of aflatoxin, upon infection with . Surprisingly, both and mutant kernels emitted greater levels of ET in response to infection by as compared with WT seed. The increased ET in single mutants was found to be due to overexpression of functional ACS genes in response to infection. Collectively, these findings suggested that ET emitted by infected seed facilitates colonization by but not aflatoxin production.
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http://dx.doi.org/10.3389/fpls.2017.00415DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5368243PMC
March 2017

In vivo diagnostics of early abiotic plant stress response via Raman spectroscopy.

Proc Natl Acad Sci U S A 2017 03 13;114(13):3393-3396. Epub 2017 Mar 13.

Institute for Quantum Science and Engineering, Texas A&M University, College Station, TX 77843;

Development of a phenotyping platform capable of noninvasive biochemical sensing could offer researchers, breeders, and producers a tool for precise response detection. In particular, the ability to measure plant stress in vivo responses is becoming increasingly important. In this work, a Raman spectroscopic technique is developed for high-throughput stress phenotyping of plants. We show the early (within 48 h) in vivo detection of plant stress responses. Coleus () plants were subjected to four common abiotic stress conditions individually: high soil salinity, drought, chilling exposure, and light saturation. Plants were examined poststress induction in vivo, and changes in the concentration levels of the reactive oxygen-scavenging pigments were observed by Raman microscopic and remote spectroscopic systems. The molecular concentration changes were further validated by commonly accepted chemical extraction (destructive) methods. Raman spectroscopy also allows simultaneous interrogation of various pigments in plants. For example, we found a unique negative correlation in concentration levels of anthocyanins and carotenoids, which clearly indicates that plant stress response is fine-tuned to protect against stress-induced damages. This precision spectroscopic technique holds promise for the future development of high-throughput screening for plant phenotyping and the quantification of biologically or commercially relevant molecules, such as antioxidants and pigments.
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http://dx.doi.org/10.1073/pnas.1701328114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5380084PMC
March 2017

Synthesis and Functions of Jasmonates in Maize.

Plants (Basel) 2016 Nov 29;5(4). Epub 2016 Nov 29.

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843, USA.

Of the over 600 oxylipins present in all plants, the phytohormone jasmonic acid (JA) remains the best understood in terms of its biosynthesis, function and signaling. Much like their eicosanoid analogues in mammalian system, evidence is growing for the role of the other oxylipins in diverse physiological processes. JA serves as the model plant oxylipin species and regulates defense and development. For several decades, the biology of JA has been characterized in a few dicot species, yet the function of JA in monocots has only recently begun to be elucidated. In this work, the synthesis and function of JA in maize is presented from the perspective of oxylipin biology. The maize genes responsible for catalyzing the reactions in the JA biosynthesis are clarified and described. Recent studies into the function of JA in maize defense against insect herbivory, pathogens and its role in growth and development are highlighted. Additionally, a list of JA-responsive genes is presented for use as biological markers for improving future investigations into JA signaling in maize.
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http://dx.doi.org/10.3390/plants5040041DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5198101PMC
November 2016

Maize death acids, 9-lipoxygenase-derived cyclopente(a)nones, display activity as cytotoxic phytoalexins and transcriptional mediators.

Proc Natl Acad Sci U S A 2015 Sep 24;112(36):11407-12. Epub 2015 Aug 24.

Section of Cell and Developmental Biology, University of California at San Diego, La Jolla, CA 92093-0380;

Plant damage promotes the interaction of lipoxygenases (LOXs) with fatty acids yielding 9-hydroperoxides, 13-hydroperoxides, and complex arrays of oxylipins. The action of 13-LOX on linolenic acid enables production of 12-oxo-phytodienoic acid (12-OPDA) and its downstream products, termed "jasmonates." As signals, jasmonates have related yet distinct roles in the regulation of plant resistance against insect and pathogen attack. A similar pathway involving 9-LOX activity on linolenic and linoleic acid leads to the 12-OPDA positional isomer, 10-oxo-11-phytodienoic acid (10-OPDA) and 10-oxo-11-phytoenoic acid (10-OPEA), respectively; however, physiological roles for 9-LOX cyclopentenones have remained unclear. In developing maize (Zea mays) leaves, southern leaf blight (Cochliobolus heterostrophus) infection results in dying necrotic tissue and the localized accumulation of 10-OPEA, 10-OPDA, and a series of related 14- and 12-carbon metabolites, collectively termed "death acids." 10-OPEA accumulation becomes wound inducible within fungal-infected tissues and at physiologically relevant concentrations acts as a phytoalexin by suppressing the growth of fungi and herbivores including Aspergillus flavus, Fusarium verticillioides, and Helicoverpa zea. Unlike previously established maize phytoalexins, 10-OPEA and 10-OPDA display significant phytotoxicity. Both 12-OPDA and 10-OPEA promote the transcription of defense genes encoding glutathione S transferases, cytochrome P450s, and pathogenesis-related proteins. In contrast, 10-OPEA only weakly promotes the accumulation of multiple protease inhibitor transcripts. Consistent with a role in dying tissue, 10-OPEA application promotes cysteine protease activation and cell death, which is inhibited by overexpression of the cysteine protease inhibitor maize cystatin-9. Unlike jasmonates, functions for 10-OPEA and associated death acids are consistent with specialized roles in local defense reactions.
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http://dx.doi.org/10.1073/pnas.1511131112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4568653PMC
September 2015

The novel monocot-specific 9-lipoxygenase ZmLOX12 is required to mount an effective jasmonate-mediated defense against Fusarium verticillioides in maize.

Mol Plant Microbe Interact 2014 Nov;27(11):1263-76

Fusarium verticillioides is a major limiting factor for maize production due to ear and stalk rot and the contamination of seed with the carcinogenic mycotoxin fumonisin. While lipoxygenase (LOX)-derived oxylipins have been implicated in defense against diverse pathogens, their function in maize resistance against F. verticillioides is poorly understood. Here, we functionally characterized a novel maize 9-LOX gene, ZmLOX12. This gene is distantly related to known dicot LOX genes, with closest homologs found exclusively in other monocot species. ZmLOX12 is predominantly expressed in mesocotyls in which it is strongly induced in response to F. verticillioides infection. The Mutator transposon-insertional lox12-1 mutant is more susceptible to F. verticillioides colonization of mesocotyls, stalks, and kernels. The infected mutant kernels accumulate a significantly greater amount of the mycotoxin fumonisin. Reduced resistance to the pathogen is accompanied by diminished levels of the jasmonic acid (JA) precursor 12-oxo phytodienoic acid, JA-isoleucine, and expression of jasmonate-biosynthetic genes. Supporting the strong defense role of jasmonates, the JA-deficient opr7 opr8 double mutant displayed complete lack of immunity to F. verticillioides. Unexpectedly, the more susceptible lox12 mutant accumulated higher levels of kauralexins, suggesting that F. verticillioides is tolerant to this group of antimicrobial phytoalexins. This study demonstrates that this unique monocot-specific 9-LOX plays a key role in defense against F. verticillioides in diverse maize tissues and provides genetic evidence that JA is the major defense hormone against this pathogen.
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http://dx.doi.org/10.1094/MPMI-06-13-0184-RDOI Listing
November 2014

Root-expressed maize lipoxygenase 3 negatively regulates induced systemic resistance to Colletotrichum graminicola in shoots.

Front Plant Sci 2013 18;4:510. Epub 2013 Dec 18.

Department of Plant Pathology and Microbiology, Texas A&M University College Station, TX, USA.

We have previously reported that disruption of a maize root-expressed 9-lipoxygenase (9-LOX) gene, ZmLOX3, results in dramatic increase in resistance to diverse leaf and stalk pathogens. Despite evident economic significance of these findings, the mechanism behind this increased resistance remained elusive. In this study, we found that increased resistance of the lox3-4 mutants is due to constitutive activation of induced systemic resistance (ISR) signaling. We showed that ZmLOX3 lacked expression in leaves in response to anthracnose leaf blight pathogen Colletotrichum graminicola, but was expressed constitutively in the roots, thus, prompting our hypothesis: the roots of lox3-4 mutants are the source of increased resistance in leaves. Supporting this hypothesis, treatment of wild-type plants (WT) with xylem sap of lox3-4 mutant induced resistance to C. graminicola to the levels comparable to those observed in lox3-4 mutant. Moreover, treating mutants with the sap collected from WT plants partially restored the susceptibility to C. graminicola. lox3-4 mutants showed primed defense responses upon infection, which included earlier and greater induction of defense-related PAL and GST genes compared to WT. In addition to the greater expression of the octadecanoid pathway genes, lox3-4 mutant responded earlier and with a greater accumulation of H2O2 in response to C. graminicola infection or treatment with alamethicin. These findings suggest that lox3-4 mutants display constitutive ISR-like signaling. In support of this idea, root colonization by Trichoderma virens strain GV29-8 induced the same level of disease resistance in WT as the treatment with the mutant sap, but had no additional resistance effect in lox3-4 mutant. While treatment with T. virens GV29 strongly and rapidly suppressed ZmLOX3 expression in hydroponically grown WT roots, T. virens Δsml mutant, which is deficient in ISR induction, was unable to suppress expression of ZmLOX3, thus, providing genetic evidence that SM1 function in ISR, at least in part, by suppressing host ZmLOX3 gene. This study and the genetic tools generated herein will allow the identification of the signals regulating the induction of resistance to aboveground attackers by beneficial soil microorganisms in the future.
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http://dx.doi.org/10.3389/fpls.2013.00510DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3867115PMC
January 2014

Two closely related members of Arabidopsis 13-lipoxygenases (13-LOXs), LOX3 and LOX4, reveal distinct functions in response to plant-parasitic nematode infection.

Mol Plant Pathol 2014 May 28;15(4):319-32. Epub 2014 Jan 28.

Department of Entomology, Nematology and Chemistry Units, Agricultural Research Organization (ARO), The Volcani Center, Bet Dagan, 50250, Israel.

The responses of two closely related members of Arabidopsis 13-lipoxygenases (13-LOXs), LOX3 and LOX4, to infection by the sedentary nematodes root-knot nematode (Meloidogyne javanica) and cyst nematode (Heterodera schachtii) were analysed in transgenic Arabidopsis seedlings. The tissue localization of LOX3 and LOX4 gene expression using β-glucuronidase (GUS) reporter gene constructs showed local induction of LOX3 expression when second-stage juveniles reached the vascular bundle and during the early stages of plant-nematode interaction through gall and syncytia formation. Thin sections of nematode-infested knots indicated LOX3 expression in mature giant cells, and high expression in neighbouring cells and those surrounding the female body. LOX4 promoter was also activated by nematode infection, although the GUS signal weakened as infection and disease progressed. Homozygous insertion mutants lacking LOX3 were less susceptible than wild-type plants to root-knot nematode infection, as reflected by a decrease in female counts. Conversely, deficiency in LOX4 function led to a marked increase in females and egg mass number and in the female to male ratio of M. javanica and H. schachtii, respectively. The susceptibility of lox4 mutants was accompanied by increased expression of allene oxide synthase, allene oxide cyclase and ethylene-responsive transcription factor 4, and the accumulation of jasmonic acid, measured in the roots of lox4 mutants. This response was not found in lox3 mutants. Taken together, our results reveal that LOX4 and LOX3 interfere differentially with distinct metabolic and signalling pathways, and that LOX4 plays a major role in controlling plant defence against nematode infection.
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http://dx.doi.org/10.1111/mpp.12094DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6638665PMC
May 2014

Characterization of genetic diversity and linkage disequilibrium of ZmLOX4 and ZmLOX5 loci in maize.

PLoS One 2013 24;8(1):e53973. Epub 2013 Jan 24.

Department of Soil and Crop Science, Texas A&M University, College Station, Texas, United States of America.

Maize (Zea mays L.) lipoxygenases (ZmLOXs) are well recognized as important players in plant defense against pathogens, especially in cross kingdom lipid communication with pathogenic fungi. This study is among the first to investigate genetic diversity at important gene paralogs ZmLOX4 and ZmLOX5. Sequencing of these genes in 400 diverse maize lines showed little genetic diversity and low linkage disequilibrium in the two genes. Importantly, we identified one inbred line in which ZmLOX5 has a disrupted open reading frame, a line missing ZmLOX5, and five lines with a duplication of ZmLOX5. Tajima's D test suggests that both ZmLOX4 and ZmLOX5 have been under neutral selection. Further investigation of haplotype data revealed that within the ZmLOX family members only ZmLOX12, a monocot specific ZmLOX, showed strong linkage disequilibrium that extends further than expected in maize. Linkage disequilibrium patterns at these loci of interest are crucial for future candidate gene association mapping studies. ZmLOX4 and ZmLOX5 mutations and copy number variants are under further investigation for crop improvement.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0053973PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3554709PMC
July 2013

The maize lipoxygenase, ZmLOX10, mediates green leaf volatile, jasmonate and herbivore-induced plant volatile production for defense against insect attack.

Plant J 2013 Apr 13;74(1):59-73. Epub 2013 Feb 13.

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843, USA.

Fatty acid derivatives are of central importance for plant immunity against insect herbivores; however, major regulatory genes and the signals that modulate these defense metabolites are vastly understudied, especially in important agro-economic monocot species. Here we show that products and signals derived from a single Zea mays (maize) lipoxygenase (LOX), ZmLOX10, are critical for both direct and indirect defenses to herbivory. We provide genetic evidence that two 13-LOXs, ZmLOX10 and ZmLOX8, specialize in providing substrate for the green leaf volatile (GLV) and jasmonate (JA) biosynthesis pathways, respectively. Supporting the specialization of these LOX isoforms, LOX8 and LOX10 are localized to two distinct cellular compartments, indicating that the JA and GLV biosynthesis pathways are physically separated in maize. Reduced expression of JA biosynthesis genes and diminished levels of JA in lox10 mutants indicate that LOX10-derived signaling is required for LOX8-mediated JA. The possible role of GLVs in JA signaling is supported by their ability to partially restore wound-induced JA levels in lox10 mutants. The impaired ability of lox10 mutants to produce GLVs and JA led to dramatic reductions in herbivore-induced plant volatiles (HIPVs) and attractiveness to parasitoid wasps. Because LOX10 is under circadian rhythm regulation, this study provides a mechanistic link to the diurnal regulation of GLVs and HIPVs. GLV-, JA- and HIPV-deficient lox10 mutants display compromised resistance to insect feeding, both under laboratory and field conditions, which is strong evidence that LOX10-dependent metabolites confer immunity against insect attack. Hence, this comprehensive gene to agro-ecosystem study reveals the broad implications of a single LOX isoform in herbivore defense.
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http://dx.doi.org/10.1111/tpj.12101DOI Listing
April 2013

Disruption of OPR7 and OPR8 reveals the versatile functions of jasmonic acid in maize development and defense.

Plant Cell 2012 Apr 20;24(4):1420-36. Epub 2012 Apr 20.

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843, USA.

Here, multiple functions of jasmonic acid (JA) in maize (Zea mays) are revealed by comprehensive analyses of JA-deficient mutants of the two oxo-phytodienoate reductase genes, OPR7 and OPR8. Single mutants produce wild-type levels of JA in most tissues, but the double mutant opr7 opr8 has dramatically reduced JA in all organs tested. opr7 opr8 displayed strong developmental defects, including formation of a feminized tassel, initiation of female reproductive buds at each node, and extreme elongation of ear shanks; these defects were rescued by exogenous JA. These data provide evidence that JA is required for male sex determination and suppression of female reproductive organ biogenesis. Moreover, opr7 opr8 exhibited delayed leaf senescence accompanied by reduced ethylene and abscisic acid levels and lack of anthocyanin pigmentation of brace roots. Remarkably, opr7 opr8 is nonviable in nonsterile soil and under field conditions due to extreme susceptibility to a root-rotting oomycete (Pythium spp), demonstrating that these genes are necessary for maize survival in nature. Supporting the importance of JA in insect defense, opr7 opr8 is susceptible to beet armyworm. Overall, this study provides strong genetic evidence for the global roles of JA in maize development and immunity to pathogens and insects.
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http://dx.doi.org/10.1105/tpc.111.094151DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3398555PMC
April 2012

A novel, conditional, lesion mimic phenotype in cotton cotyledons due to the expression of an endochitinase gene from Trichoderma virens.

Plant Sci 2012 Feb 15;183:86-95. Epub 2011 Nov 15.

Institute for Plant Genomics and Biotechnology, Texas A&M University, College Station, TX 77843-2123, USA.

We have observed a novel, lesion mimic phenotype (LMP) in the cotyledons of cotton seedlings expressing an endochitinase gene from Trichoderma virens. This phenotype, however, is conditional and is elicited only when the transgenic seedlings are germinating on a medium that is devoid of mineral nutrients. The LMP manifests itself around the 5th day in the form of scattered, dry necrotic lesions on the cotyledons. The severity of the LMP is correlated with the level of transgene activity. Production of reactive oxygen species and activities of certain defense related enzymes and genes were substantially higher in the cotyledons of seedlings that were growing under mineral nutrient stress. Molecular and biochemical analyses indicated significantly higher-level activities of certain defense-related genes/enzymes at the onset of the phenotype. Treatment with methyl jasmonate can induce LMP in the cotyledons of wild-type (WT) seedlings similar to that observed in the endochitinase-expressing seedlings grown on nutrient-free medium. On the other hand, salicylic acid (SA), its functional analog, benzo(1,2,3) thiadiazole-7-carbothioic acid (BTH), and ibuprofen can rescue the LMP induced by the seedling-growth on nutrient-deficient medium. Nutrient deficiency-induced activation of a defense response appears to be the contributing factor in the development of LMP in endochitinase-expressing cotton seedlings.
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http://dx.doi.org/10.1016/j.plantsci.2011.11.005DOI Listing
February 2012

Regulators of G-protein signalling in Fusarium verticillioides mediate differential host-pathogen responses on nonviable versus viable maize kernels.

Mol Plant Pathol 2011 Jun 7;12(5):479-91. Epub 2011 Jan 7.

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843-2132, USA.

GBB1, a heterotrimeric G-protein β-subunit gene, was shown to be a key regulator of fumonisin B(1) (FB(1) ) biosynthesis in the maize pathogen Fusarium verticillioides. In this study, we performed functional analyses of genes that encode putative RGS (regulators of G-protein signalling) proteins and PhLPs (phosducin-like proteins) in F. verticillioides. These proteins are known to regulate heterotrimeric G-protein activity by altering the intrinsic guanosine triphosphatase (GTPase) activity, which, in turn, influences the signalling mechanisms that control fungal growth, virulence and secondary metabolism. Our aim was to isolate and characterize gene(s) that are under the transcriptional control of GBB1, and to test the hypothesis that these genes are directly associated with FB(1) regulation and fungal development in F. verticillioides on maize kernels. We first identified eight genes (two PhLPs and six RGSs) in the F. verticillioides genome, and a subsequent transcriptional expression study revealed that three RGS genes were up-regulated in the gbb1 deletion (Δgbb1) mutant and one RGS gene was up-regulated in the wild-type. To characterize their function, we generated knockout mutants using a homologous recombination strategy. When grown on autoclaved nonviable kernels, two mutants (ΔflbA2 and ΔrgsB) produced significantly higher levels of FB(1) compared with the wild-type progenitor, suggesting that the two mutated genes are negative regulators of FB(1) biosynthesis. ΔflbA2 also showed a severe curly conidia germination pattern, which was contradictory to that observed in the Δgbb1 strain. Strikingly, when these mutants were grown on live maize kernels, we observed contrasting FB(1) and conidiation phenotypes in fungal mutants, which strongly suggests that these G-protein regulators have an impact on how F. verticillioides responds to host/environmental factors. Our data also provide evidence that fungal G-protein signalling is important for modulating the ethylene biosynthetic pathway in maize kernels.
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http://dx.doi.org/10.1111/j.1364-3703.2010.00686.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6640359PMC
June 2011

The lipid language of plant-fungal interactions.

Fungal Genet Biol 2011 Jan 16;48(1):4-14. Epub 2010 May 16.

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, 2132 TAMU, TX, United States.

Lipid mediated cross-kingdom communication between hosts and pathogens is a rapidly emerging field in molecular plant-fungal interactions. Amidst our growing understanding of fungal and plant chemical cross-talk lies the distinct, yet little studied, role for a group of oxygenated lipids derived from polyunsaturated fatty acids, termed oxylipins. Endogenous fungal oxylipins are known for their roles in carrying out pathogenic strategies to successfully colonize their host, reproduce, and synthesize toxins. While plant oxylipins also have functions in reproduction and development, they are largely recognized as agents that facilitate resistance to pathogen attack. Here we review the composition and endogenous functions of oxylipins produced by both plants and fungi and introduce evidence which suggests that fungal pathogens exploit host oxylipins to facilitate their own virulence and pathogenic development. Specifically, we describe how fungi induce plant lipid metabolism to utilize plant oxylipins in order to promote G-protein-mediated regulation of sporulation and mycotoxin production in the fungus. The use of host-ligand mimicry (i.e. coronatine) to manipulate plant defense responses that benefit the fungus are also implicated.
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http://dx.doi.org/10.1016/j.fgb.2010.05.005DOI Listing
January 2011
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