Publications by authors named "Tesfaye Mengiste"

49 Publications

Transcriptome analysis of early stages of sorghum grain mold disease reveals defense regulators and metabolic pathways associated with resistance.

BMC Genomics 2021 Apr 22;22(1):295. Epub 2021 Apr 22.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, 47907, USA.

Background: Sorghum grain mold is the most important disease of the crop. The disease results from simultaneous infection of the grain by multiple fungal species. Host responses to these fungi and the underlying molecular and cellular processes are poorly understood. To understand the genetic, molecular and biochemical components of grain mold resistance, transcriptome profiles of the developing grain of resistant and susceptible sorghum genotypes were studied.

Results: The developing kernels of grain mold resistant RTx2911 and susceptible RTx430 sorghum genotypes were inoculated with a mixture of fungal pathogens mimicking the species complexity of the disease under natural infestation. Global transcriptome changes corresponding to multiple molecular and cellular processes, and biological functions including defense, secondary metabolism, and flavonoid biosynthesis were observed with differential regulation in the two genotypes. Genes encoding pattern recognition receptors (PRRs), regulators of growth and defense homeostasis, antimicrobial peptides, pathogenesis-related proteins, zein seed storage proteins, and phytoalexins showed increased expression correlating with resistance. Notably, SbLYK5 gene encoding an orthologue of chitin PRR, defensin genes SbDFN7.1 and SbDFN7.2 exhibited higher expression in the resistant genotype. The SbDFN7.1 and SbDFN7.2 genes are tightly linked and transcribed in opposite orientation with a likely common bidirectional promoter. Interestingly, increased expression of JAZ and other transcriptional repressors were observed that suggested the tight regulation of plant defense and growth. The data suggest a pathogen inducible defense system in the developing grain of sorghum that involves the chitin PRR, MAPKs, key transcription factors, downstream components regulating immune gene expression and accumulation of defense molecules. We propose a model through which the biosynthesis of 3-deoxyanthocynidin phytoalexins, defensins, PR proteins, other antimicrobial peptides, and defense suppressing proteins are regulated by a pathogen inducible defense system in the developing grain.

Conclusions: The transcriptome data from a rarely studied tissue shed light into genetic, molecular, and biochemical components of disease resistance and suggested that the developing grain shares conserved immune response mechanisms but also components uniquely enriched in the grain. Resistance was associated with increased expression of genes encoding regulatory factors, novel grain specific antimicrobial peptides including defensins and storage proteins that are potential targets for crop improvement.
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http://dx.doi.org/10.1186/s12864-021-07609-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8063297PMC
April 2021

The Botrytis cinerea Crh1 transglycosylase is a cytoplasmic effector triggering plant cell death and defense response.

Nat Commun 2021 04 12;12(1):2166. Epub 2021 Apr 12.

School of Plant Sciences and Food Security, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.

Crh proteins catalyze crosslinking of chitin and glucan polymers in fungal cell walls. Here, we show that the BcCrh1 protein from the phytopathogenic fungus Botrytis cinerea acts as a cytoplasmic effector and elicitor of plant defense. BcCrh1 is localized in vacuoles and the endoplasmic reticulum during saprophytic growth. However, upon plant infection, the protein accumulates in infection cushions; it is then secreted to the apoplast and translocated into plant cells, where it induces cell death and defense responses. Two regions of 53 and 35 amino acids are sufficient for protein uptake and cell death induction, respectively. BcCrh1 mutant variants that are unable to dimerize lack transglycosylation activity, but are still able to induce plant cell death. Furthermore, Arabidopsis lines expressing the bccrh1 gene exhibit reduced sensitivity to B. cinerea, suggesting a potential use of the BcCrh1 protein in plant immunization against this necrotrophic pathogen.
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http://dx.doi.org/10.1038/s41467-021-22436-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8042016PMC
April 2021

Genome-wide association analysis reveals seed protein loci as determinants of variations in grain mold resistance in sorghum.

Theor Appl Genet 2021 Apr 16;134(4):1167-1184. Epub 2021 Jan 16.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, 47907, USA.

Key Message: GWAS analysis revealed variations at loci harboring seed storage, late embryogenesis abundant protein, and a tannin biosynthesis gene associated with sorghum grain mold resistance. Grain mold is the most important disease of sorghum [Sorghum bicolor (L.) Moench]. It starts at the early stages of grain development due to concurrent infection by multiple fungal species. The genetic architecture of resistance to grain mold is poorly understood. Using a diverse set of 635 Ethiopian sorghum accessions, we conducted a multi-stage disease rating for resistance to grain mold under natural infestation in the field. Through genome-wide association analyses with 173,666 SNPs and multiple models, two novel loci were identified that were consistently associated with grain mold resistance across environments. Sequence variation at new loci containing sorghum KAFIRIN gene encoding a seed storage protein affecting seed texture and LATE EMBRYOGENESIS ABUNDANT 3 (LEA3) gene encoding a protein that accumulates in seeds, previously implicated in stress tolerance, were significantly associated with grain mold resistance. The KAFIRIN and LEA3 loci were also significant factors in grain mold resistance in accessions with non-pigmented grains. Moreover, we consistently detected the known SNP (S4_62316425) in TAN1 gene, a regulator of tannin accumulation in sorghum grain to be significantly associated with grain mold resistance. Identification of loci associated with new mechanisms of resistance provides fresh insight into genetic control of the trait, while the highly resistant accessions can serve as sources of resistance genes for breeding. Overall, our association data suggest the critical role of loci harboring seed protein genes and implicate grain chemical and physical properties in sorghum grain mold resistance.
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http://dx.doi.org/10.1007/s00122-020-03762-2DOI Listing
April 2021

Tomato Domestication Attenuated Responsiveness to a Beneficial Soil Microbe for Plant Growth Promotion and Induction of Systemic Resistance to Foliar Pathogens.

Front Microbiol 2020 18;11:604566. Epub 2020 Dec 18.

Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN, United States.

Crop domestication events followed by targeted breeding practices have been pivotal for improvement of desirable traits and to adapt cultivars to local environments. Domestication also resulted in a strong reduction in genetic diversity among modern cultivars compared to their wild relatives, though the effect this could have on tripartite relationships between plants, belowground beneficial microbes and aboveground pathogens remains undetermined. We quantified plant growth performance, basal resistance and induced systemic resistance (ISR) by , a beneficial soil microbe against , a necrotrophic fungus and , a hemi-biotrophic oomycete, in 25 diverse tomato genotypes. Wild tomato related species, tomato landraces and modern commercial cultivars that were conventionally or organically bred, together, representing a domestication gradient were evaluated. Relationships between basal and ISR, plant physiological status and phenolic compounds were quantified to identify potential mechanisms. enhanced shoot and root biomass and ISR to both pathogens in a genotype specific manner. Moreover, improvements in plant performance in response to gradually decreased along the domestication gradient. Wild relatives and landraces were more responsive to , resulting in greater suppression of foliar pathogens than modern cultivars. Photosynthetic rate and stomatal conductance of some tomato genotypes were improved by treatment whereas leaf nitrogen status of the majority of tomato genotypes were not altered. There was a negative relationship between basal resistance and induced resistance for both diseases, and a positive correlation between -ISR to and enhanced total flavonoid contents. These findings suggest that domestication and breeding practices have altered plant responsiveness to beneficial soil microbes. Further studies are needed to decipher the molecular mechanisms underlying the differential promotion of plant growth and resistance among genotypes, and identify molecular markers to integrate selection for responsiveness into future breeding programs.
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http://dx.doi.org/10.3389/fmicb.2020.604566DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7775394PMC
December 2020

A comprehensive phenotypic and genomic characterization of Ethiopian sorghum germplasm defines core collection and reveals rich genetic potential in adaptive traits.

Plant Genome 2020 11 17;13(3):e20055. Epub 2020 Sep 17.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, 47907, USA.

Understanding population genetic structure and diversity of a crop is essential in designing selection strategies in plant breeding. About 2010 Ethiopian sorghum accessions were phenotyped for different traits at multiple locations. A subset of the collection, 1628 accessions, predominantly landraces, some improved varieties, and inbred lines were genotyped by sequencing. Phenotypic data revealed association of important traits with different sorghum growing agro-climatic regions, high genetic diversity and the presence of rare natural variation in the Ethiopian sorghum germplasm. Subsequent genotypic analysis determined optimum number of sub-populations, distinct cluster groups and ancestries of each sorghum accessions. To improve utilization of germplasm, a core subset of 387 lines were selected following posteriori grouping of genotypes based on cluster groups obtained through GBS analysis followed by stratified random sampling using quantitative traits. In order to evaluate how well this new sorghum and millet innovation lab (SMIL) collection from Ethiopia is represented within the largest world sorghum collection at United States Department of Agriculture - National Plant Germplasm System (USDA-NPGS) and the sorghum association panel (SAP), comparisons were conducted based on SNP data. The SMIL collection displayed high genetic diversity with some redundancy with the USDA-NPGS germplasm but SAP showed clear distinction. Furthermore, genome-environment association analysis identified candidate genes associated with adaptation to abiotic factors, that will be important for exploitation of adaptive potential to different environments. In summary, our results described the diversity and relationship of sorghum collections, representativeness of developed core and provide novel insights into candidate genes associated to abiotic stress tolerance.
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http://dx.doi.org/10.1002/tpg2.20055DOI Listing
November 2020

Global mRNA and microRNA expression dynamics in response to anthracnose infection in sorghum.

BMC Genomics 2020 Nov 3;21(1):760. Epub 2020 Nov 3.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, 47907, USA.

Background: Anthracnose is a damaging disease of sorghum caused by the fungal pathogen Colletotrichum sublineolum. Genome-wide mRNA and microRNA (miRNA) profiles of resistant and susceptible sorghum genotypes were studied to understand components of immune responses, and fungal induced miRNA and target gene networks.

Results: A total of 18 mRNA and 12 miRNA libraries from resistant and susceptible sorghum lines were sequenced prior to and after inoculation with C. sublineolum. Significant differences in transcriptomes of the susceptible and resistant genotypes were observed with dispersion distance and hierarchical cluster tree analyses. Of the total 33,032 genes predicted in the sorghum genome, 19,593 were induced by C. sublineolum, and 15,512 were differentially expressed (DEGs) between the two genotypes. The resistant line was marked by significant reprogramming of the transcriptome at 24 h post inoculation (hpi), and a decrease at 48 hpi, whereas the susceptible line displayed continued changes in gene expression concordant with elevated fungal growth in the susceptible genotype. DEGs encode proteins implicated in diverse functions including photosynthesis, synthesis of tetrapyrrole, carbohydrate and secondary metabolism, immune signaling, and chitin binding. Genes encoding immune receptors, MAPKs, pentatricopeptide repeat proteins, and WRKY transcription factors were induced in the resistant genotype. In a parallel miRNA profiling, the susceptible line displayed greater number of differentially expressed miRNAs than the resistant line indicative of a widespread suppression of gene expression. Interestingly, we found 75 miRNAs, including 36 novel miRNAs, which were differentially expressed in response to fungal inoculation. The expression of 50 miRNAs was significantly different between resistant and susceptible lines. Subsequently, for 35 differentially expressed miRNAs, the corresponding 149 target genes were identified. Expression of 56 target genes were significantly altered after inoculation, showing inverse expression with the corresponding miRNAs.

Conclusions: We provide insights into genome wide dynamics of mRNA and miRNA profiles, biological and cellular processes underlying host responses to fungal infection in sorghum. Resistance is correlated with early transcriptional reprogramming of genes in various pathways. Fungal induced genes, miRNAs and their targets with a potential function in host responses to anthracnose were identified, opening avenues for genetic dissection of resistance mechanisms.
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http://dx.doi.org/10.1186/s12864-020-07138-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7641857PMC
November 2020

Changes in the core endophytic mycobiome of carrot taproots in response to crop management and genotype.

Sci Rep 2020 08 13;10(1):13685. Epub 2020 Aug 13.

Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN, USA.

Fungal endophytes can influence production and post-harvest challenges in carrot, though the identity of these microbes as well as factors affecting their composition have not yet been determined, which prevents growers from managing these organisms to improve crop performance. Consequently, we characterized the endophytic mycobiome in the taproots of three carrot genotypes that vary in resistance to two pathogens grown in a trial comparing organic and conventional crop management using Illumina sequencing of the internal transcribed spacer (ITS) gene. A total of 1,480 individual operational taxonomic units (OTUs) were identified. Most were consistent across samples, indicating that they are part of a core mycobiome, though crop management influenced richness and diversity, likely in response to differences in soil properties. There were also differences in individual OTUs among genotypes and the nematode resistant genotype was most responsive to management system indicating that it has greater control over its endophytic mycobiome, which could potentially play a role in resistance. Members of the Ascomycota were most dominant, though the exact function of most taxa remains unclear. Future studies aimed at overcoming difficulties associated with isolating fungal endophytes are needed to identify these microbes at the species level and elucidate their specific functional roles.
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http://dx.doi.org/10.1038/s41598-020-70683-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7426841PMC
August 2020

CDK8 is associated with RAP2.6 and SnRK2.6 and positively modulates abscisic acid signaling and drought response in Arabidopsis.

New Phytol 2020 12 2;228(5):1573-1590. Epub 2020 Aug 2.

Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN, 47907, USA.

CDK8 is a key subunit of Mediator complex, a large multiprotein complex that is a fundamental part of the conserved eukaryotic transcriptional machinery. However, the biological functions of CDK8 in plant abiotic stress responses remain largely unexplored. Here, we demonstrated CDK8 as a critical regulator in the abscisic acid (ABA) signaling and drought response pathways in Arabidopsis. Compared to wild-type, cdk8 mutants showed reduced sensitivity to ABA, impaired stomatal apertures and hypersensitivity to drought stress. Transcriptomic and chromatin immunoprecipitation analysis revealed that CDK8 positively regulates the transcription of several ABA-responsive genes, probably through promoting the recruitment of RNA polymerase II to their promoters. We discovered that both CDK8 and SnRK2.6 interact physically with an ERF/AP2 transcription factor RAP2.6, which can directly bind to the promoters of RD29A and COLD-REGULATED 15A (COR15A) with GCC or DRE elements, thereby promoting their expression. Importantly, we also showed that CDK8 is essential for the ABA-induced expression of RAP2.6 and RAP2.6-mediated upregulation of ABA-responsive genes, indicating that CDK8 could link the SnRK2.6-mediated ABA signaling to RNA polymerase II to promote immediate transcriptional response to ABA and drought signals. Overall, our data provide new insights into the roles of CDK8 in modulating ABA signaling and drought responses.
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http://dx.doi.org/10.1111/nph.16787DOI Listing
December 2020

Crop management system and carrot genotype affect endophyte composition and Alternaria dauci suppression.

PLoS One 2020 4;15(6):e0233783. Epub 2020 Jun 4.

Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana, United State of America.

Managing pests in carrot production is challenging. Endophytic microbes have been demonstrated to improve the health and productivity of many crops, but factors affecting endophyte dynamics in carrot is still not well understood. The goal of this study was to determine how crop management system and carrot genotype interact to affect the composition and potential of endophytes to mitigate disease caused by Alternaria dauci, an important carrot pathogen. Twenty-eight unique isolates were collected from the taproots of nine diverse genotypes of carrot grown in a long-term trial comparing organic and conventional management. Antagonistic activity was quantified using an in vitro assay, and potential for individual isolates to mitigate disease was evaluated in greenhouse trials using two carrot cultivars. Results confirm that carrot taproots are colonized by an abundant and diverse assortment of bacteria and fungi representing at least distinct 13 genera. Soils in the organic system had greater total organic matter, microbial biomass and activity than the conventional system and endophyte composition in taproots grown in this system were more abundant and diverse, and had greater antagonistic activity. Carrot genotype also affected endophyte abundance as well as potential for individual isolates to affect seed germination, seedling growth and tolerance to A. dauci. The benefits of endophytes on carrot growth were greatest when plants were subject to A. dauci stress, highlighting the importance of environmental conditions in the functional role of endophytes. Results of this study provide evidence that endophytes can play an important role in improving carrot performance and mediating resistance to A. dauci, and it may someday be possible to select for these beneficial plant-microbial relationships in carrot breeding programs. Implementing soil-building practices commonly used in organic farming systems has potential to promote these beneficial relationships and improve the health and productivity of carrot crops.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0233783PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7272071PMC
August 2020

A Large-Scale Genome-Wide Association Analyses of Ethiopian Sorghum Landrace Collection Reveal Loci Associated With Important Traits.

Front Plant Sci 2019 29;10:691. Epub 2019 May 29.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, United States.

The eastern Africa region, Ethiopia and its surroundings, is considered as the center of origin and diversity for sorghum, and has contributed to global sorghum genetic improvement. The germplasm from this region harbors enormous genetic variation for various traits but little is known regarding the genetic architecture of most traits. Here, 1425 Ethiopian landrace accessions were phenotyped under field conditions for presence or absence of awns, panicle compactness and shape, panicle exsertion, pericarp color, glume cover, plant height and smut resistance under diverse environmental conditions in Ethiopia. In addition, F1 hybrids obtained from a subset of 1341 accessions crossed to an A1 cytoplasmic male sterile line, ATx623, were scored for fertility/sterility reactions. Subsequently, genotyping-by-sequencing generated a total of 879,407 SNPs from which 72,190 robust SNP markers were selected after stringent quality control (QC). Pairwise distance-based hierarchical clustering identified 11 distinct groups. Of the genotypes assigned to either one of the 11 sub-populations, 65% had high ancestry membership coefficient with the likelihood of more than 0.60 and the remaining 35% represented highly admixed accessions. A genome-wide association study (GWAS) identified loci and SNPs associated with aforementioned traits. GWAS based on compressed mixed linear model (CMLM) identified SNPs with significant association (FDR ≤ 0.05) to the different traits studied. The percentage of total phenotypic variation explained with significant SNPs across traits ranged from 2 to 43%. Candidate genes showing significant association with different traits were identified. The sorghum transcription factor, was identified as a strong candidate gene conditioning male fertility. Notably, sorghum CLAVATA1 receptor like kinase, known for regulation of plant growth, and the gene RAP2-7, known to suppress transition to flowering, were significantly associated with plant height. In addition, the like MYB transcription factor and showed strong association with pericarp color validating previous observations. Overall, the genetic architecture of natural variation representing the complex Ethiopian sorghum germplasm was established. The study contributes to the characterization of genes and alleles controlling agronomic traits, and will serve as a source of markers for molecular breeding.
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http://dx.doi.org/10.3389/fpls.2019.00691DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6549537PMC
May 2019

NPR1 Promotes Its Own and Target Gene Expression in Plant Defense by Recruiting CDK8.

Plant Physiol 2019 09 20;181(1):289-304. Epub 2019 May 20.

Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208

NPR1 (NONEXPRESSER OF PR GENES1) functions as a master regulator of the plant hormone salicylic acid (SA) signaling and plays an essential role in plant immunity. In the nucleus, NPR1 interacts with transcription factors to induce the expression of (-) genes and thereby promote defense responses. However, the underlying molecular mechanism of gene activation is poorly understood. Furthermore, despite the importance of NPR1 in plant immunity, the regulation of expression has not been extensively studied. Here, we show that SA promotes the interaction of NPR1 with both CDK8 (CYCLIN-DEPENDENT KINASE8) and WRKY18 (WRKY DNA-BINDING PROTEIN18) in Arabidopsis (). NPR1 recruits CDK8 and WRKY18 to the promoter, facilitating its own expression. Intriguingly, CDK8 and its associated Mediator subunits positively regulate and expression and play a pivotal role in local and systemic immunity. Moreover, CDK8 interacts with WRKY6, WRKY18, and TGA transcription factors and brings RNA polymerase II to and promoters and coding regions to facilitate their expression. Our studies reveal a mechanism in which NPR1 recruits CDK8, WRKY18, and TGA transcription factors along with RNA polymerase II in the presence of SA and thereby facilitates its own and target gene expression for the establishment of plant immunity.
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http://dx.doi.org/10.1104/pp.19.00124DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6716257PMC
September 2019

Endosidin2-14 Targets the Exocyst Complex in Plants and Fungal Pathogens to Inhibit Exocytosis.

Plant Physiol 2019 07 9;180(3):1756-1770. Epub 2019 May 9.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907

The evolutionarily conserved octameric exocyst complex tethers secretory vesicles to the site of membrane fusion during exocytosis. The plant exocyst complex functions in cell wall biosynthesis, polarized growth, stress responses, and hormone signaling. In fungal pathogens, the exocyst complex is required for growth, development, and pathogenesis. Endosidin2 (ES2) is known to inhibit exocytosis in plant and mammalian cells by targeting the EXO70 subunit of the exocyst complex. Here we show that an analog of ES2, ES2-14, targets plant and two fungal EXO70s. A lower dosage of ES2-14 than of ES2 is required to inhibit plant growth, plant exocytic trafficking, and fungal growth. ES2-14 treatments inhibit appressorium formation and reduce lesion sizes caused by Inhibition of EXO70 by ES2-14 in also reduces its virulence in Arabidopsis (). Interestingly, ES2-14 did not affect EXO70 localization or transferrin recycling in mammalian cells. Overall, our results indicate that a minor change in ES2 affects its specificity in targeting EXO70s in different organisms and they demonstrate the potential of using ES2-14 to study the mechanisms of plant and fungal exocytosis and the roles of exocytosis in fungus-plant interactions.
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http://dx.doi.org/10.1104/pp.18.01457DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6752926PMC
July 2019

Tomato PEPR1 ORTHOLOG RECEPTOR-LIKE KINASE1 Regulates Responses to Systemin, Necrotrophic Fungi, and Insect Herbivory.

Plant Cell 2018 09 21;30(9):2214-2229. Epub 2018 Aug 21.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907

Endogenous peptides regulate plant immunity and growth. Systemin, a peptide specific to the Solanaceae, is known for its functions in plant responses to insect herbivory and pathogen infections. Here, we describe the identification of the tomato () PEPR1/2 ORTHOLOG RECEPTOR-LIKE KINASE1 (PORK1) as the TOMATO PROTEIN KINASE1b (TPK1b) interacting protein and demonstrate its biological functions in systemin signaling and tomato immune responses. Tomato RNA interference (RNAi) plants with significantly reduced expression showed increased susceptibility to tobacco hornworm (), reduced seedling growth sensitivity to the systemin peptide, and compromised systemin-mediated resistance to Systemin-induced expression of (), a classical marker for systemin signaling, was abrogated in RNAi plants. Similarly, in response to systemin and wounding, the expression of jasmonate pathway genes was attenuated in RNAi plants. TPK1b, a key regulator of tomato defense against and , was phosphorylated by PORK1. Interestingly, wounding- and systemin-induced phosphorylation of TPK1b was attenuated when expression was suppressed. Our data suggest that resistance to and is dependent on PORK1-mediated responses to systemin and subsequent phosphorylation of TPK1b. Altogether, PORK1 regulates tomato systemin, wounding, and immune responses.
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http://dx.doi.org/10.1105/tpc.17.00908DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6181013PMC
September 2018

and Its Homologs Are Not Required for -Mediated Transformation, but Play a Role in and Salt Stress Responses.

Front Plant Sci 2018 12;9:749. Epub 2018 Jun 12.

Department of Biological Sciences, Purdue University, West Lafayette, IN, United States.

The bZIP transcription factor VIP1 interacts with the virulence protein VirE2, but the role of VIP1 in -mediated transformation remains controversial. Previously tested mutant plants produce a truncated protein containing the crucial bZIP DNA-binding domain. We generated the CRISPR/Cas mutant that lacks this domain. The transformation susceptibility of and wild-type plants is similar. Because of potential functional redundancy among VIP1 homologs, we tested transgenic lines expressing VIP1 fused to a SRDX repression domain. All VIP1-SRDX transgenic lines showed wild-type levels of transformation, indicating that neither VIP1 nor its homologs are required for -mediated transformation. Because VIP1 is involved in innate immune response signaling, we tested the susceptibility of mutant and plants to and . mutant and plants show increased susceptibility to but not to infection, suggesting a role for VIP1 in , but not in , defense signaling. susceptibility is dependent on abscisic acid (ABA) which is also important for abiotic stress responses. The germination of mutant and seeds is sensitive to exogenous ABA, suggesting a role for VIP1 in response to ABA. mutant and plants show increased tolerance to growth in salt, indicating a role for VIP1 in response to salt stress.
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http://dx.doi.org/10.3389/fpls.2018.00749DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6005860PMC
June 2018

Epigenetic switch from repressive to permissive chromatin in response to cold stress.

Proc Natl Acad Sci U S A 2018 06 21;115(23):E5400-E5409. Epub 2018 May 21.

Department of Biomedical Science and Engineering, Konkuk University, 05029 Seoul, South Korea;

Switching from repressed to active status in chromatin regulation is part of the critical responses that plants deploy to survive in an ever-changing environment. We previously reported that HOS15, a WD40-repeat protein, is involved in histone deacetylation and cold tolerance in However, it remained unknown how HOS15 regulates cold responsive genes to affect cold tolerance. Here, we show that HOS15 interacts with histone deacetylase 2C (HD2C) and both proteins together associate with the promoters of cold-responsive genes, and Cold induced HD2C degradation is mediated by the CULLIN4 (CUL4)-based E3 ubiquitin ligase complex in which HOS15 acts as a substrate receptor. Interference with the association of HD2C and the gene promoters by HOS15 correlates with increased acetylation levels of histone H3. HOS15 also interacts with CBF transcription factors to modulate cold-induced binding to the gene promoters. Our results here demonstrate that cold induces HOS15-mediated chromatin modifications by degrading HD2C. This switches the chromatin structure status and facilitates recruitment of CBFs to the gene promoters. This is an apparent requirement to acquire cold tolerance.
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http://dx.doi.org/10.1073/pnas.1721241115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6003311PMC
June 2018

Mutation in sorghum alters strigolactones and causes resistance.

Proc Natl Acad Sci U S A 2017 04 10;114(17):4471-4476. Epub 2017 Apr 10.

Department of Agronomy, Purdue University, West Lafayette, IN 47907;

is a major biotic constraint to sorghum production in semiarid tropical Africa and Asia. Genetic resistance to this parasitic weed is the most economically feasible control measure. Mutant alleles at the () locus drastically reduce germination stimulant activity. We provide evidence that the responsible gene at codes for an enzyme annotated as a sulfotransferase and show that functional loss of this gene results in a change of the dominant strigolactone (SL) in root exudates from 5-deoxystrigol, a highly active germination stimulant, to orobanchol, an SL with opposite stereochemistry. Orobanchol, although not previously reported in sorghum, functions in the multiple SL roles required for normal growth and environmental responsiveness but does not stimulate germination of This work describes the identification of a gene regulating resistance and the underlying protective chemistry resulting from mutation.
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http://dx.doi.org/10.1073/pnas.1618965114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5410831PMC
April 2017

Global Regulation of Plant Immunity by Histone Lysine Methyl Transferases.

Plant Cell 2016 07 27;28(7):1640-61. Epub 2016 Jun 27.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907

Posttranslational modification of histones modulates gene expression affecting diverse biological functions. We showed that the Arabidopsis thaliana histone methyl transferases SET DOMAIN GROUP8 (SDG8) and SDG25 regulate pep1-, flg22-, and effector-triggered immunity as well as systemic acquired resistance. Genome-wide basal and induced transcriptome changes regulated by SDG8 and/or SDG25 showed that two genes of the SDG-dependent transcriptome, CAROTENOID ISOMERASE2 (CCR2) and ECERIFERUM3 (CER3), were also required for plant immunity, establishing mechanisms in defense functions for SDG8 and SDG25. CCR2 catalyzes the biosynthesis of carotenoids, whereas CER3 is involved in the biosynthesis of cuticular wax. SDG8 and SDG25 affected distinct and overlapping global and locus-specific histone H3 lysine 4 (H3K4) and histone H3 lysine 36 (H3K36) methylations. Loss of immunity in sdg mutants was attributed to altered global and CCR2- and CER3-specific histone lysine methylation (HLM). Loss of immunity in sdg, ccr2, and cer3 mutants was also associated with diminished accumulation of lipids and loss of cuticle integrity. In addition, sdg8 and sdg25 mutants were impaired in H2B ubiquitination (H2Bubn) at CCR2, CER3, and H2Bubn regulated R gene, SNC1, revealing crosstalk between the two types of histone modifications. In summary, SDG8 and SDG25 contribute to plant immunity directly through HLM or indirectly through H2Bubn and by regulating expression of plant immunity genes, accumulation of lipids, biosynthesis of carotenoids, and maintenance of cuticle integrity.
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http://dx.doi.org/10.1105/tpc.16.00012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4981126PMC
July 2016

Arabidopsis HOOKLESS1 Regulates Responses to Pathogens and Abscisic Acid through Interaction with MED18 and Acetylation of WRKY33 and ABI5 Chromatin.

Plant Cell 2016 07 17;28(7):1662-81. Epub 2016 Jun 17.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907

Arabidopsis thaliana HOOKLESS1 (HLS1) encodes a putative histone acetyltransferase with known functions in seedling growth. Here, we show that HLS1 regulates plant responses to pathogens and abscisic acid (ABA) through histone acetylation at chromatin of target loci. The hls1 mutants show impaired responses to bacterial and fungal infection, accelerated senescence, and impaired responses to ABA. HLS1 modulates the expression of WRKY33 and ABA INSENSITIVE5 (ABI5), known regulators of pathogen and ABA responses, respectively, through direct association with these loci. Histone 3 acetylation (H3Ac), a positive mark of transcription, at WRKY33 and ABI5 requires HLS1 function. ABA treatment and pathogen infection enhance HLS1 recruitment and H3Ac at WRKY33. HLS1 associates with Mediator, a eukaryotic transcription coregulatory complex, through direct interaction with mediator subunit 18 (MED18), with which it shares multiple functions. HLS1 recruits MED18 to the WRKY33 promoter, boosting WKRY33 expression, suggesting the synergetic action of HLS1 and MED18. By contrast, MED18 recruitment to ABI5 and transcriptional activation are independent of HLS1. ABA-mediated priming of resistance to fungal infection was abrogated in hls1 and wrky33 mutants but correlated with ABA-induced HLS1 accumulation. In sum, HLS1 provides a regulatory node in pathogen and hormone response pathways through interaction with the Mediator complex and important transcription factors.
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http://dx.doi.org/10.1105/tpc.16.00105DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4981130PMC
July 2016

Limited Addition of the 6-Arm β1,2-linked N-Acetylglucosamine (GlcNAc) Residue Facilitates the Formation of the Largest N-Glycan in Plants.

J Biol Chem 2015 Jul 22;290(27):16560-72. Epub 2015 May 22.

From the Division of Applied Life Science and Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, 501 Jinju-daero, Jinju 660-701, Korea,

The most abundant N-glycan in plants is the paucimannosidic N-glycan with core β1,2-xylose and α1,3-fucose residues (Man3XylFuc(GlcNAc)2). Here, we report a mechanism in Arabidopsis thaliana that efficiently produces the largest N-glycan in plants. Genetic and biochemical evidence indicates that the addition of the 6-arm β1,2-GlcNAc residue by N-acetylglucosaminyltransferase II (GnTII) is less effective than additions of the core β1,2-xylose and α1,3-fucose residues by XylT, FucTA, and FucTB in Arabidopsis. Furthermore, analysis of gnt2 mutant and 35S:GnTII transgenic plants shows that the addition of the 6-arm non-reducing GlcNAc residue to the common N-glycan acceptor GlcNAcMan3(GlcNAc)2 inhibits additions of the core β1,2-xylose and α1,3-fucose residues. Our findings indicate that plants limit the rate of the addition of the 6-arm GlcNAc residue to the common N-glycan acceptor as a mechanism to facilitate formation of the prevalent N-glycans with Man3XylFuc(GlcNAc)2 and (GlcNAc)2Man3XylFuc(GlcNAc)2 structures.
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http://dx.doi.org/10.1074/jbc.M115.653162DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4505410PMC
July 2015

Pathogen associated molecular pattern (PAMP)-triggered immunity is compromised under C-limited growth.

Mol Cells 2015 Jan 12;38(1):40-50. Epub 2014 Nov 12.

Division of Applied Life Science (BK21 Plus Program) and Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju 660-701, Korea.

In the interaction between plants and pathogens, carbon (C) resources provide energy and C skeletons to maintain, among many functions, the plant immune system. However, variations in C availability on pathogen associated molecular pattern (PAMP) triggered immunity (PTI) have not been systematically examined. Here, three types of starch mutants with enhanced susceptibility to Pseudomonas syringae pv. tomato DC3000 hrcC were examined for PTI. In a dark period-dependent manner, the mutants showed compromised induction of a PTI marker, and callose accumulation in response to the bacterial PAMP flagellin, flg22. In combination with weakened PTI responses in wild type by inhibition of the TCA cycle, the experiments determined the necessity of C-derived energy in establishing PTI. Global gene expression analyses identified flg22 responsive genes displaying C supply-dependent patterns. Nutrient recycling-related genes were regulated similarly by C-limitation and flg22, indicating re-arrangements of expression programs to redirect resources that establish or strengthen PTI. Ethylene and NAC transcription factors appear to play roles in these processes. Under C-limitation, PTI appears compromised based on suppression of genes required for continued biosynthetic capacity and defenses through flg22. Our results provide a foundation for the intuitive perception of the interplay between plant nutrition status and pathogen defense.
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http://dx.doi.org/10.14348/molcells.2015.2165DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4314131PMC
January 2015

CYCLIN-DEPENDENT KINASE8 differentially regulates plant immunity to fungal pathogens through kinase-dependent and -independent functions in Arabidopsis.

Plant Cell 2014 Oct 3;26(10):4149-70. Epub 2014 Oct 3.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907

CYCLIN-DEPENDENT KINASE8 (CDK8) is a widely studied component of eukaryotic Mediator complexes. However, the biological and molecular functions of plant CDK8 are not well understood. Here, we provide evidence for regulatory functions of Arabidopsis thaliana CDK8 in defense and demonstrate its functional and molecular interactions with other Mediator and non-Mediator subunits. The cdk8 mutant exhibits enhanced resistance to Botrytis cinerea but susceptibility to Alternaria brassicicola. The contributions of CDK8 to the transcriptional activation of defensin gene PDF1.2 and its interaction with MEDIATOR COMPLEX SUBUNIT25 (MED25) implicate CDK8 in jasmonate-mediated defense. Moreover, CDK8 associates with the promoter of AGMATINE COUMAROYLTRANSFERASE to promote its transcription and regulate the biosynthesis of the defense-active secondary metabolites hydroxycinnamic acid amides. CDK8 also interacts with the transcription factor WAX INDUCER1, implying its additional role in cuticle development. In addition, overlapping functions of CDK8 with MED12 and MED13 and interactions between CDK8 and C-type cyclins suggest the conserved configuration of the plant Mediator kinase module. In summary, while CDK8's positive transcriptional regulation of target genes and its phosphorylation activities underpin its defense functions, the impaired defense responses in the mutant are masked by its altered cuticle, resulting in specific resistance to B. cinerea.
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http://dx.doi.org/10.1105/tpc.114.128611DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4247566PMC
October 2014

Resistance to Botrytis cinerea in Solanum lycopersicoides involves widespread transcriptional reprogramming.

BMC Genomics 2014 May 3;15:334. Epub 2014 May 3.

Department of Plant Pathology, University of Arkansas Division of Agriculture, 217 Plant Sciences, Fayetteville, AR 72701, USA.

Background: Tomato (Solanum lycopersicum), one of the world's most important vegetable crops, is highly susceptible to necrotrophic fungal pathogens such as Botrytis cinerea and Alternaria solani. Improving resistance through conventional breeding has been hampered by a shortage of resistant germplasm and difficulties in introgressing resistance into elite germplasm without linkage drag. The goal of this study was to explore natural variation among wild Solanum species to identify new sources of resistance to necrotrophic fungi and dissect mechanisms underlying resistance against B. cinerea.

Results: Among eight wild species evaluated for resistance against B. cinerea and A. solani, S. lycopersicoides expressed the highest levels of resistance against both pathogens. Resistance against B. cinerea manifested as containment of pathogen growth. Through next-generation RNA sequencing and de novo assembly of the S. lycopersicoides transcriptome, changes in gene expression were analyzed during pathogen infection. In response to B. cinerea, differentially expressed transcripts grouped into four categories: genes whose expression rapidly increased then rapidly decreased, genes whose expression rapidly increased and plateaued, genes whose expression continually increased, and genes with decreased expression. Homology-based searches also identified a limited number of highly expressed B. cinerea genes. Almost immediately after infection by B. cinerea, S. lycopersicoides suppressed photosynthesis and metabolic processes involved in growth, energy generation, and response to stimuli, and simultaneously induced various defense-related genes, including pathogenesis-related protein 1 (PR1), a beta-1,3-glucanase (glucanase), and a subtilisin-like protease, indicating a shift in priority towards defense. Moreover, cluster analysis revealed novel, uncharacterized genes that may play roles in defense against necrotrophic fungal pathogens in S. lycopersicoides. The expression of orthologous defense-related genes in S. lycopersicum after infection with B. cinerea revealed differences in the onset and intensity of induction, thus illuminating a potential mechanism explaining the increased susceptibility. Additionally, metabolic pathway analyses identified putative defense-related categories of secondary metabolites.

Conclusions: In sum, this study provided insight into resistance against necrotrophic fungal pathogens in the Solanaceae, as well as novel sequence resources for S. lycopersicoides.
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http://dx.doi.org/10.1186/1471-2164-15-334DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4035065PMC
May 2014

The Arabidopsis Myb transcription factor MTF1 is a unidirectional regulator of susceptibility to Agrobacterium.

Plant Signal Behav 2014 Apr 30;9. Epub 2014 Apr 30.

Department of Biological Sciences; Purdue University; West Lafayette, IN USA.

We recently described the Arabidopsis Myb transcription factor MTF1 that negatively regulates plant susceptibility to Agrobacterium-mediated transformation. Roots of mtf1 mutant plants show increased susceptibility to several Agrobacterium strains, and complementing the mutants with a MTF1 cDNA decreases transformation susceptibility to wild-type levels. Here, we show that overexpression of MTF1 in a wild-type Arabidopsis background does not result in altered transformation susceptibility. However, MTF1 overexpressing plants show increased root length and larger and darker leaves, indicating that MTF1 plays a role in plant growth and development. MTF1 decreases Arabidopsis root susceptibility specifically to Agrobacterium but plant responses to the pathogens Alternaria brassicicola or Pseudomonas syringae pv Tomato were not altered. However, the homozygous MTF1 mutant mtf1-4 is resistant to Botrytis cinerea strain BO5-10 and is regulated through the ethylene signaling pathway mediated by upregulation of the AP2/ERF transcription factor ORA59.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4091474PMC
April 2014

MED18 interaction with distinct transcription factors regulates multiple plant functions.

Nat Commun 2014 ;5:3064

Department of Botany and Plant Pathology, Purdue University, 915 W State Street, West Lafayette, Indiana 47907, USA.

Mediator is an evolutionarily conserved transcriptional regulatory complex. Mechanisms of Mediator function are poorly understood. Here we show that Arabidopsis MED18 is a multifunctional protein regulating plant immunity, flowering time and responses to hormones through interactions with distinct transcription factors. MED18 interacts with YIN YANG1 to suppress disease susceptibility genes glutaredoxins GRX480, GRXS13 and thioredoxin TRX-h5. Consequently, yy1 and med18 mutants exhibit deregulated expression of these genes and enhanced susceptibility to fungal infection. In addition, MED18 interacts with ABA INSENSITIVE 4 and SUPPRESSOR OF FRIGIDA4 to regulate abscisic acid responses and flowering time, respectively. MED18 associates with the promoter, coding and terminator regions of target genes suggesting its function in transcription initiation, elongation and termination. Notably, RNA polymerase II occupancy and histone H3 lysine tri-methylation of target genes are affected in the med18 mutant, reinforcing MED18 function in different mechanisms of transcriptional control. Overall, MED18 conveys distinct cues to engender transcription underpinning plant responses.
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http://dx.doi.org/10.1038/ncomms4064DOI Listing
November 2015

Genetic and cellular mechanisms regulating plant responses to necrotrophic pathogens.

Curr Opin Plant Biol 2013 Aug 13;16(4):505-12. Epub 2013 Jul 13.

Purdue University, Department of Botany and Plant Pathology, 915 W. State Street, West Lafayette, IN 47907, United States.

Necrotrophs are plant pathogens that kill host cells and proliferate on nutrients from dead or dying tissues causing devastating diseases of horticultural and agronomic crops. Their interactions with plants involve a complex network of pathogen disease factors and corresponding plant immune response regulators. Mechanisms of quantitative resistance and the major regulators intersect regardless of pathogen life style. By contrast, some plant immune responses, such as effector-triggered immunity (ETI), a major source of qualitative resistance to biotrophs, are co-opted by necrotrophs to promote disease, which highlights the disparate plant immunity systems. Advances towards understanding mechanisms and processes underlying host responses to necrotrophs are summarized.
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http://dx.doi.org/10.1016/j.pbi.2013.06.014DOI Listing
August 2013

Inverse modulation of plant immune and brassinosteroid signaling pathways by the receptor-like cytoplasmic kinase BIK1.

Proc Natl Acad Sci U S A 2013 Jul 1;110(29):12114-9. Epub 2013 Jul 1.

Key Laboratory of Biopesticide and Chemical Biology, Ministry of Education, Fujian Agriculture and Forestry University, Fuzhou 350002, China.

Maintaining active growth and effective immune responses is often costly for a living organism to survive. Fine-tuning the shared cross-regulators is crucial for metazoans and plants to make a trade-off between growth and immunity. The Arabidopsis regulatory receptor-like kinase BAK1 complexes with the receptor kinases FLS2 in bacterial flagellin-triggered immunity and BRI1 in brassinosteroid (BR)-mediated growth. BR homeostasis and signaling unidirectionally modulate FLS2-mediated immune responses at multiple levels. We have shown previously that BIK1, a receptor-like cytoplasmic kinase, is directly phosphorylated by BAK1 and associates with FLS2/BAK1 complex in transducing flagellin signaling. In contrast to its positive role in plant immunity, we report here that BIK1 acts as a negative regulator in BR signaling. The bik1 mutant displays various BR hypersensitive phenotypes accompanied with increased accumulation of de-phosphorylated BES1 proteins and transcriptional regulation of BZR1 and BES1 target genes. BIK1 associates with BRI1, and is released from BRI1 receptor upon BR treatment, which is reminiscent of FLS2-BIK1 complex dynamics in flagellin signaling. The ligand-induced release of BIK1 from receptor complexes is associated with BIK1 phosphorylation. However, in contrast to BAK1-dependent FLS2-BIK1 dissociation, BAK1 is dispensable for BRI1-BIK1 dissociation. Unlike FLS2 signaling which depends on BAK1 to phosphorylate BIK1, BRI1 directly phosphorylates BIK1 to transduce BR signaling. Thus, BIK1 relays the signaling in plant immunity and BR-mediated growth via distinct phosphorylation by BAK1 and BRI1, respectively. Our studies indicate that BIK1 mediates inverse functions in plant immunity and development via dynamic association with specific receptor complexes and differential phosphorylation events.
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http://dx.doi.org/10.1073/pnas.1302154110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3718091PMC
July 2013

Quiescent and necrotrophic lifestyle choice during postharvest disease development.

Annu Rev Phytopathol 2013 13;51:155-76. Epub 2013 May 13.

Department of Postharvest Science of Fresh Produce, ARO, Volcani Center, Bet Dagan, 50250 Israel.

Insidious fungal infections by postharvest pathogens remain quiescent during fruit growth until, at a particular phase during fruit ripening and senescence, the pathogens switch to the necrotrophic lifestyle and cause decay. During ripening, fruits undergo physiological processes, such as activation of ethylene biosynthesis, cuticular changes, and cell-wall loosening-changes that are accompanied by a decline of antifungal compounds, both those that are preformed and those that are inducible secondary metabolites. Pathogen infection of the unripe host fruit initiates defensive signal-transduction cascades, culminating in accumulation of antifungal proteins that limit fungal growth and development. In contrast, development of the same pathogens during fruit ripening and storage activates a substantially different signaling network, one that facilitates aggressive fungal colonization. This review focuses on responses induced by the quiescent pathogens of postharvest diseases in unripe host fruits. New genome-scale experimental approaches have begun to delineate the complex and multiple networks of host and pathogen responses activated to maintain or to facilitate the transition from the quiescent to the necrotrophic lifestyle.
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http://dx.doi.org/10.1146/annurev-phyto-082712-102349DOI Listing
December 2013

Plant immunity to necrotrophs.

Authors:
Tesfaye Mengiste

Annu Rev Phytopathol 2012 15;50:267-94. Epub 2012 Jun 15.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907, USA.

Plants inhabit environments crowded with infectious microbes that pose constant threats to their survival. Necrotrophic pathogens are notorious for their aggressive and wide-ranging virulence strategies that promote host cell death and acquire nutrients for growth and reproduction from dead cells. This lifestyle constitutes the axis of their pathogenesis and virulence strategies and marks contrasting immune responses to biotrophic pathogens. The diversity of virulence strategies in necrotrophic species corresponds to multifaceted host immune response mechanisms. When effective, the plant immune system disarms the infectious necrotroph of its pathogenic arsenal or attenuates its effect, restricting further ingress and disease symptom development. Simply inherited resistance traits confer protection against host-specific necrotrophs (HSNs), whereas resistance to broad host-range necrotrophs (BHNs) is complex. Components of host genetic networks, as well as the molecular and cellular processes that mediate host immune responses to necrotrophs, are being identified. In this review, recent advances in our understanding of plant immune responses to necrotrophs and comparison with responses to biotrophic pathogens are summarized, highlighting common and contrasting mechanisms.
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http://dx.doi.org/10.1146/annurev-phyto-081211-172955DOI Listing
August 2014

Polyamines attenuate ethylene-mediated defense responses to abrogate resistance to Botrytis cinerea in tomato.

Plant Physiol 2012 Feb 29;158(2):1034-45. Epub 2011 Nov 29.

Department of Horticulture and Landscape Architecture, Center for Plant Environmental Stress Physiology, Purdue University, West Lafayette, Indiana 47907, USA.

Transgenic tomato (Solanum lycopersicum) lines overexpressing yeast spermidine synthase (ySpdSyn), an enzyme involved in polyamine (PA) biosynthesis, were developed. These transgenic lines accumulate higher levels of spermidine (Spd) than the wild-type plants and were examined for responses to the fungal necrotrophs Botrytis cinerea and Alternaria solani, bacterial pathogen Pseudomonas syringae pv tomato DC3000, and larvae of the chewing insect tobacco hornworm (Manduca sexta). The Spd-accumulating transgenic tomato lines were more susceptible to B. cinerea than the wild-type plants; however, responses to A. solani, P. syringae, or M. sexta were similar to the wild-type plants. Exogenous application of ethylene precursors, S-adenosyl-Met and 1-aminocyclopropane-1-carboxylic acid, or PA biosynthesis inhibitors reversed the response of the transgenic plants to B. cinerea. The increased susceptibility of the ySpdSyn transgenic tomato to B. cinerea was associated with down-regulation of gene transcripts involved in ethylene biosynthesis and signaling. These data suggest that PA-mediated susceptibility to B. cinerea is linked to interference with the functions of ethylene in plant defense.
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http://dx.doi.org/10.1104/pp.111.188698DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3271740PMC
February 2012

Biochemical and genetic requirements for function of the immune response regulator BOTRYTIS-INDUCED KINASE1 in plant growth, ethylene signaling, and PAMP-triggered immunity in Arabidopsis.

Plant Cell 2011 Aug 23;23(8):2831-49. Epub 2011 Aug 23.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907, USA.

Arabidopsis thaliana BOTRYTIS-INDUCED KINASE1 (BIK1) regulates immune responses to a distinct class of pathogens. Here, mechanisms underlying BIK1 function and its interactions with other immune response regulators were determined. We describe BIK1 function as a component of ethylene (ET) signaling and PAMP-triggered immunity (PTI) to fungal pathogens. BIK1 in vivo kinase activity increases in response to flagellin peptide (flg22) and the ET precursor 1-aminocyclopropane-1-carboxylic acid (ACC) but is blocked by inhibition of ET perception. BIK1 induction by flg22, ACC, and pathogens is strictly dependent on EIN3, and the bik1 mutation results in altered expression of ET-regulated genes. BIK1 site-directed mutants were used to determine residues essential for phosphorylation and biological functions in planta, including PTI, ET signaling, and plant growth. Genetic analysis revealed flg22-induced PTI to Botrytis cinerea requires BIK1, EIN2, and HUB1 but not genes involved in salicylate (SA) functions. BIK1-mediated PTI to Pseudomonas syringae is modulated by SA, ET, and jasmonate signaling. The coi1 mutation suppressed several bik1 phenotypes, suggesting that COI1 may act as a repressor of BIK1 function. Thus, common and distinct mechanisms underlying BIK1 function in mediating responses to distinct pathogens are uncovered. In sum, the critical role of BIK1 in plant immune responses hinges upon phosphorylation, its function in ET signaling, and complex interactions with other immune response regulators.
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http://dx.doi.org/10.1105/tpc.111.087122DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3180795PMC
August 2011