Publications by authors named "Zhibing Lai"

19 Publications

  • Page 1 of 1

Transcriptome analysis of the role of autophagy in plant response to heat stress.

PLoS One 2021 26;16(2):e0247783. Epub 2021 Feb 26.

National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, China.

Autophagy plays a critical role in plant heat tolerance in part by targeting heat-induced nonnative proteins for degradation. Autophagy also regulates metabolism, signaling and other processes and it is less understood how the broad function of autophagy affects plant heat stress responses. To address this issue, we performed transcriptome profiling of Arabidopsis wild-type and autophagy-deficient atg5 mutant in response to heat stress. A large number of differentially expressed genes (DEGs) were identified between wild-type and atg5 mutant even under normal conditions. These DEGs are involved not only in metabolism, hormone signaling, stress responses but also in regulation of nucleotide processing and DNA repair. Intriguingly, we found that heat treatment resulted in more robust changes in gene expression in wild-type than in the atg5 mutant plants. The dampening effect of autophagy deficiency on heat-regulated gene expression was associated with already altered expression of many heat-regulated DEGs prior to heat stress in the atg5 mutant. Altered expression of a large number of genes involved in metabolism and signaling in the autophagy mutant prior to heat stress may affect plant response to heat stress. Furthermore, autophagy played a positive role in the expression of defense- and stress-related genes during the early stage of heat stress responses but had little effect on heat-induced expression of heat shock genes. Taken together, these results indicate that the broad role of autophagy in metabolism, cellular homeostasis and other processes can also potentially affect plant heat stress responses and heat tolerance.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0247783PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7909648PMC
February 2021

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition).

Autophagy 2021 Jan 8;17(1):1-382. Epub 2021 Feb 8.

University of Crete, School of Medicine, Laboratory of Clinical Microbiology and Microbial Pathogenesis, Voutes, Heraklion, Crete, Greece; Foundation for Research and Technology, Institute of Molecular Biology and Biotechnology (IMBB), Heraklion, Crete, Greece.

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.
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http://dx.doi.org/10.1080/15548627.2020.1797280DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7996087PMC
January 2021

Functional analysis of tomato CHIP ubiquitin E3 ligase in heat tolerance.

Sci Rep 2021 Jan 18;11(1):1713. Epub 2021 Jan 18.

Department of Landscape and Horticulture, Ecology College, Lishui University, Lishui, 323000, Zhejiang, China.

Plants have evolved genetic and physiological mechanisms to mitigate the adverse effects of high temperature. CARBOXYL TERMINUS OF THE HSC70-INTERACTING PROTEINS (CHIP) is a conserved chaperone-dependent ubiquitin E3 ligase that targets misfolded proteins. Here, we report functional analysis of the SlCHIP gene from tomato (Solanum lycopersicum) in heat tolerance. SlCHIP encodes a CHIP protein with three tandem tetracopeptide repeat (TPR) motifs and a C-terminal U box domain. Phylogenetic analysis of CHIP homologs from animals, spore-bearing and seed plants revealed a tree topology similar to the evolutionary tree of the organisms. Expression of SlCHIP was induced under high temperature and was also responsive to plant stress hormones. Silencing of SlCHIP in tomato reduced heat tolerance based on increased heat stress symptoms, reduced photosynthetic activity, elevated electrolyte leakage and accumulation of insoluble protein aggregates. The accumulated protein aggregates in SlCHIP-silenced plants were still highly ubiquitinated, suggesting involvement of other E3 ligases in ubiquitination. SlCHIP restored the heat tolerance of Arabidopsis chip mutant to the wild type levels. These results indicate that tomato SlCHIP plays a critical role in heat stress responses most likely by targeting degradation of misfolded proteins that are generated during heat stress.
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http://dx.doi.org/10.1038/s41598-021-81372-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7814054PMC
January 2021

Phosphorylation of ATG18a by BAK1 suppresses autophagy and attenuates plant resistance against necrotrophic pathogens.

Autophagy 2020 Aug 26:1-18. Epub 2020 Aug 26.

National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, China.

Autophagy is critical for plant defense against necrotrophic pathogens, which causes serious yield loss on crops. However, the post-translational regulatory mechanisms of autophagy pathway in plant resistance against necrotrophs remain poorly understood. In this study, we report that phosphorylation modification on ATG18a, a key regulator of autophagosome formation in , constitutes a post-translation regulation of autophagy, which attenuates plant resistance against necrotrophic pathogens. We found that phosphorylation of ATG18a suppresses autophagosome formation and its subsequent delivery into the vacuole, which results in reduced autophagy activity and compromised plant resistance against . In contrast, overexpression of ATG18a dephosphorylation-mimic form increases the accumulation of autophagosomes and complements the plant resistance of mutant against . Moreover, BAK1, a key regulator in plant resistance, was identified to physically interact with and phosphorylate ATG18a. Mutation of blocks ATG18a phosphorylation at four of the five detected phosphorylation sites after infection and strongly activates autophagy, leading to enhanced resistance against . Collectively, the identification of functional phosphorylation sites on ATG18a and the corresponding kinase BAK1 unveiled how plant regulates autophagy during resistance against necrotrophic pathogens.

Abbreviations: : the cauliflower mosaic virus promoter; ; ABA: abscisic acid; ATG: autophagy-related; ATG18a: autophagy-related protein 18a in ; ATG8a: autophagy-related protein 8a in ; ATG8-PE: ATG8 conjugated with PE; ; BAK1: Brassinosteroid insensitive 1-associated receptor kinase1 in ; BiFC: biomolecular fluorescence complementation; BIK1: Botrytis-insensitive kinase 1 in ; BKK1: BAK1-like 1 in ; BR: brassinosteroid; Co-IP: coimmunoprecipitation; dai: days after inoculation; DAMPs: damage-associated molecular patterns; ; ER: endoplasmic reticulum; ETI: effector-triggered immunity; GFP: green fluorescent protein; HA: hemagglutinin; IP: immunoprecipitation; LC-MS/MS: liquid chromatography-tandem mass spectrometry; LCI: luciferase complementation imaging; MPK3: mitogen-activated protein kinase 3 in ; MPK4: mitogen-activated protein kinase 4 in ; MPK6: mitogen-activated protein kinase 6 in ; NES: nuclear export sequence; PAMP: pathogen-associated molecular pattern; PCR: polymerase chain reaction; PE: phosphatidylethanolamine; PRR: pattern recognition receptor; PtdIns(3,5)P phosphatidylinositol (3,5)-biphosphate; PtdIns3P: phosphatidylinositol 3-biphosphate; PTI: PAMP-triggered immunity; qRT-PCR: quantitative reverse transcription PCR; SnRK2.6: SNF1-related protein kinase 2.6 in ; TORC1: the rapamycin-sensitive Tor complex1; TRAF: tumor necrosis factor receptor-associated factor; WT: wild type plant; Yc: C-terminal fragment of YFP; YFP: yellow fluorescent protein; Yn: N-terminal fragment of YFP.
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http://dx.doi.org/10.1080/15548627.2020.1810426DOI Listing
August 2020

Copper Ions are Required for in Appressorium Formation and Virulence on Maize.

Phytopathology 2020 Feb 5;110(2):494-504. Epub 2019 Dec 5.

National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, China.

is the causal agent of southern corn leaf blight, a destructive disease on maize worldwide. However, how it regulates virulence on maize is still largely unknown. Here, we report that two copper transporter genes, and , are required for its virulence. and mutants showed attenuated virulence on maize compared with the wild-type strain TM17 but development phenotypes of those mutants on media with or without infection-related stress agents were the same as the wild-type strain. Moreover, and play critical roles in appressorium formation and mutation of or suppresses the appressorium formation. Furthermore, copper-chelating agent ammonium tetrathiomolybdate suppressed the appressorium formation and virulence of on maize, whereas copper ions enhanced the appressorium formation and virulence on maize. The results indicate that copper ions are required for appressorium formation and virulence of on maize and are acquired from the environment by two copper transporters: ChCTR1 and ChCTR4.
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http://dx.doi.org/10.1094/PHYTO-07-19-0254-RDOI Listing
February 2020

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

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

Arabidopsis sigma factor binding proteins are activators of the WRKY33 transcription factor in plant defense.

Plant Cell 2011 Oct 11;23(10):3824-41. Epub 2011 Oct 11.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907-2054, USA.

Necrotrophic pathogens are important plant pathogens that cause many devastating plant diseases. Despite their impact, our understanding of the plant defense response to necrotrophic pathogens is limited. The WRKY33 transcription factor is important for plant resistance to necrotrophic pathogens; therefore, elucidation of its functions will enhance our understanding of plant immunity to necrotrophic pathogens. Here, we report the identification of two WRKY33-interacting proteins, nuclear-encoded SIGMA FACTOR BINDING PROTEIN1 (SIB1) and SIB2, which also interact with plastid-encoded plastid RNA polymerase SIGMA FACTOR1. Both SIB1 and SIB2 contain an N-terminal chloroplast targeting signal and a putative nuclear localization signal, suggesting that they are dual targeted. Bimolecular fluorescence complementation indicates that WRKY33 interacts with SIBs in the nucleus of plant cells. Both SIB1 and SIB2 contain a short VQ motif that is important for interaction with WRKY33. The two VQ motif-containing proteins recognize the C-terminal WRKY domain and stimulate the DNA binding activity of WRKY33. Like WRKY33, both SIB1 and SIB2 are rapidly and strongly induced by the necrotrophic pathogen Botrytis cinerea. Resistance to B. cinerea is compromised in the sib1 and sib2 mutants but enhanced in SIB1-overexpressing transgenic plants. These results suggest that dual-targeted SIB1 and SIB2 function as activators of WRKY33 in plant defense against necrotrophic pathogens.
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http://dx.doi.org/10.1105/tpc.111.090571DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3229152PMC
October 2011

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

A critical role of autophagy in plant resistance to necrotrophic fungal pathogens.

Plant J 2011 Jun 4;66(6):953-68. Epub 2011 Apr 4.

Department of Botany and Plant Pathology, 915 West State Street, Purdue University, West Lafayette, IN 47907-2054, USA.

Autophagy is a pathway for degradation of cytoplasmic components. In plants, autophagy plays an important role in nutrient recycling during nitrogen or carbon starvation, and in responses to abiotic stress. Autophagy also regulates age- and immunity-related programmed cell death, which is important in plant defense against biotrophic pathogens. Here we show that autophagy plays a critical role in plant resistance to necrotrophic pathogens. ATG18a, a critical autophagy protein in Arabidopsis, interacts with WRKY33, a transcription factor that is required for resistance to necrotrophic pathogens. Expression of autophagy genes and formation of autophagosomes are induced in Arabidopsis by the necrotrophic fungal pathogen Botrytis cinerea. Induction of ATG18a and autophagy by B. cinerea was compromised in the wrky33 mutant, which is highly susceptible to necrotrophic pathogens. Arabidopsis mutants defective in autophagy exhibit enhanced susceptibility to the necrotrophic fungal pathogens B. cinerea and Alternaria brassicicola based on increased pathogen growth in the mutants. The hypersusceptibility of the autophagy mutants was associated with reduced expression of the jasmonate-regulated PFD1.2 gene, accelerated development of senescence-like chlorotic symptoms, and increased protein degradation in infected plant tissues. These results strongly suggest that autophagy cooperates with jasmonate- and WRKY33-mediated signaling pathways in the regulation of plant defense responses to necrotrophic pathogens.
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http://dx.doi.org/10.1111/j.1365-313X.2011.04553.xDOI Listing
June 2011

Roles of arabidopsis WRKY18, WRKY40 and WRKY60 transcription factors in plant responses to abscisic acid and abiotic stress.

BMC Plant Biol 2010 Dec 19;10:281. Epub 2010 Dec 19.

State Key Laboratory of Biocontrol and Key Laboratory of Gene Engineering of the Ministry of Education, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China.

Background: WRKY transcription factors are involved in plant responses to both biotic and abiotic stresses. Arabidopsis WRKY18, WRKY40, and WRKY60 transcription factors interact both physically and functionally in plant defense responses. However, their role in plant abiotic stress response has not been directly analyzed.

Results: We report that the three WRKYs are involved in plant responses to abscisic acid (ABA) and abiotic stress. Through analysis of single, double, and triple mutants and overexpression lines for the WRKY genes, we have shown that WRKY18 and WRKY60 have a positive effect on plant ABA sensitivity for inhibition of seed germination and root growth. The same two WRKY genes also enhance plant sensitivity to salt and osmotic stress. WRKY40, on the other hand, antagonizes WRKY18 and WRKY60 in the effect on plant sensitivity to ABA and abiotic stress in germination and growth assays. Both WRKY18 and WRKY40 are rapidly induced by ABA, while induction of WRKY60 by ABA is delayed. ABA-inducible expression of WRKY60 is almost completely abolished in the wrky18 and wrky40 mutants. WRKY18 and WRKY40 recognize a cluster of W-box sequences in the WRKY60 promoter and activate WRKY60 expression in protoplasts. Thus, WRKY60 might be a direct target gene of WRKY18 and WRKY40 in ABA signaling. Using a stable transgenic reporter/effector system, we have shown that both WRKY18 and WRKY60 act as weak transcriptional activators while WRKY40 is a transcriptional repressor in plant cells.

Conclusions: We propose that the three related WRKY transcription factors form a highly interacting regulatory network that modulates gene expression in both plant defense and stress responses by acting as either transcription activator or repressor.
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http://dx.doi.org/10.1186/1471-2229-10-281DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3023790PMC
December 2010

A first genome assembly of the barley fungal pathogen Pyrenophora teres f. teres.

Genome Biol 2010 10;11(11):R109. Epub 2010 Nov 10.

Department of Environment and Agriculture, Curtin University, Kent Street, Bentley, Perth, Western Australia 6102, Australia.

Background: Pyrenophora teres f. teres is a necrotrophic fungal pathogen and the cause of one of barley's most important diseases, net form of net blotch. Here we report the first genome assembly for this species based solely on short Solexa sequencing reads of isolate 0-1. The assembly was validated by comparison to BAC sequences, ESTs, orthologous genes and by PCR, and complemented by cytogenetic karyotyping and the first genome-wide genetic map for P. teres f. teres.

Results: The total assembly was 41.95 Mbp and contains 11,799 gene models of 50 amino acids or more. Comparison against two sequenced BACs showed that complex regions with a high GC content assembled effectively. Electrophoretic karyotyping showed distinct chromosomal polymorphisms between isolates 0-1 and 15A, and cytological karyotyping confirmed the presence of at least nine chromosomes. The genetic map spans 2477.7 cM and is composed of 243 markers in 25 linkage groups, and incorporates simple sequence repeat markers developed from the assembly. Among predicted genes, non-ribosomal peptide synthetases and efflux pumps in particular appear to have undergone a P. teres f. teres-specific expansion of non-orthologous gene families.

Conclusions: This study demonstrates that paired-end Solexa sequencing can successfully capture coding regions of a filamentous fungal genome. The assembly contains a plethora of predicted genes that have been implicated in a necrotrophic lifestyle and pathogenicity and presents a significant resource for examining the bases for P. teres f. teres pathogenicity.
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http://dx.doi.org/10.1186/gb-2010-11-11-r109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3156948PMC
June 2011

The Arabidopsis Botrytis Susceptible1 Interactor defines a subclass of RING E3 ligases that regulate pathogen and stress responses.

Plant Physiol 2010 Dec 4;154(4):1766-82. Epub 2010 Oct 4.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907-2054, USA.

We studied the function of Arabidopsis (Arabidopsis thaliana) Botrytis Susceptible1 Interactor (BOI) in plant responses to pathogen infection and abiotic stress. BOI physically interacts with and ubiquitinates Arabidopsis BOS1, an R2R3MYB transcription factor previously implicated in stress and pathogen responses. In transgenic plants expressing the BOS1-β-glucuronidase transgene, β-glucuronidase activity could be detected only after inhibition of the proteosome, suggesting that BOS1 is a target of ubiquitin-mediated degradation by the proteosome. Plants with reduced BOI transcript levels generated through RNA interference (BOI RNAi) were more susceptible to the necrotrophic fungus Botrytis cinerea and less tolerant to salt stress. In addition, BOI RNAi plants exhibited increased cell death induced by the phytotoxin α-picolinic acid and by a virulent strain of the bacterial pathogen Pseudomonas syringae, coincident with peak disease symptoms. However, the hypersensitive cell death associated with different race-specific resistance genes was unaffected by changes in the level of BOI transcript. BOI expression was enhanced by B. cinerea and salt stress but repressed by the plant hormone gibberellin, indicating a complex regulation of BOI gene expression. Interestingly, BOI RNAi plants exhibit reduced growth responsiveness to gibberellin. We also present data revealing the function of three Arabidopsis BOI-RELATED GENES (BRGs), which contribute to B. cinerea resistance and the suppression of disease-associated cell death. In sum, BOI and BRGs represent a subclass of RING E3 ligases that contribute to plant disease resistance and abiotic stress tolerance through the suppression of pathogen-induced as well as stress-induced cell death.
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http://dx.doi.org/10.1104/pp.110.163915DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2996010PMC
December 2010

Functional analysis of the Arabidopsis PAL gene family in plant growth, development, and response to environmental stress.

Plant Physiol 2010 Aug 21;153(4):1526-38. Epub 2010 Jun 21.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907-2054, USA.

Phenylalanine ammonia-lyase (PAL) catalyzes the first step of the phenylpropanoid pathway, which produces precursors to a variety of important secondary metabolites. Arabidopsis (Arabidopsis thaliana) contains four PAL genes (PAL1-PAL4), but there has been no genetic analysis to assess the biological functions of the entire gene family. Here, we report the generation and analysis of combined mutations for the four Arabidopsis PAL genes. Contrary to a previous report, we found that three independent pal1 pal2 double mutants were fertile and generated yellow seeds due to the lack of condensed tannin pigments in the seed coat. The pal1 pal2 double mutants were also deficient in anthocyanin pigments in various plant tissues, which accumulate in wild-type plants under stress conditions. Thus, PAL1 and PAL2 have a redundant role in flavonoid biosynthesis. Furthermore, the pal1 pal2 double mutants were more sensitive to ultraviolet-B light but more tolerant to drought than wild-type plants. We have also generated two independent pal1 pal2 pal3 pal4 quadruple knockout mutants, which are stunted and sterile. The quadruple knockout mutants still contained about 10% of the wild-type PAL activity, which might result from one or more leaky pal mutant genes or from other unknown PAL genes. The quadruple mutants also accumulated substantially reduced levels of salicylic acid and displayed increased susceptibility to a virulent strain of the bacterial pathogen Pseudomonas syringae. These results provide further evidence for both distinct and overlapping roles of the Arabidopsis PAL genes in plant growth, development, and responses to environmental stresses.
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http://dx.doi.org/10.1104/pp.110.157370DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2923909PMC
August 2010

Biosynthesis of salicylic acid in plants.

Plant Signal Behav 2009 Jun 12;4(6):493-6. Epub 2009 Jun 12.

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

Salicylic acid (SA) is an important signal molecule in plants. Two pathways of SA biosynthesis have been proposed in plants. Biochemical studies using isotope feeding have suggested that plants synthesize SA from cinnamate produced by the activity of phenylalanine ammonia lyase (PAL). Silencing of PAL genes in tobacco or chemical inhibition of PAL activity in Arabidopsis, cucumber and potato reduces pathogen-induced SA accumulation. Genetic studies, on the other hand, indicate that the bulk of SA is produced from isochorismate. In bacteria, SA is synthesized from chorismate through two reactions catalyzed by isochorismate synthase (ICS) and isochorismate pyruvate lyase (IPL). Arabidopsis contains two ICS genes but has no gene encoding proteins similar to the bacterial IPL. Thus, how SA is synthesized in plants is not fully elucidated. Two recently identified Arabidopsis genes, PBS3 and EPS1, are important for pathogen-induced SA accumulation. PBS3 encodes a member of the acyl-adenylate/thioester-forming enzyme family and EPS1 encodes a member of the BAHD acyltransferase superfamily. PBS3 and EPS1 may be directly involved in the synthesis of an important precursor or regulatory molecule for SA biosynthesis. The pathways and regulation of SA biosynthesis in plants may be more complicated than previously thought.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2688294PMC
http://dx.doi.org/10.4161/psb.4.6.8392DOI Listing
June 2009

Arabidopsis WRKY38 and WRKY62 transcription factors interact with histone deacetylase 19 in basal defense.

Plant Cell 2008 Sep 5;20(9):2357-71. Epub 2008 Sep 5.

Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907-2054, USA.

Arabidopsis thaliana WRKY38 and WRKY62, encoding two structurally similar type III WRKY transcription factors, are induced in a Nonexpressor of PR Gene1 (NPR1)-dependent manner by salicylic acid (SA) or by virulent Pseudomonas syringae. Disease resistance and SA-regulated Pathogenesis-Related1 (PR1) gene expression are enhanced in the wrky38 and wrky62 single mutants and, to a greater extent, in the double mutants. Overexpression of WRKY38 or WRKY62 reduces disease resistance and PR1 expression. Thus, WRKY38 and WRKY62 function additively as negative regulators of plant basal defense. WRKY38 and WRKY62 interact with Histone Deacetylase 19 (HDA19). Expression of HDA19 is also induced by P. syringae, and the stability of its induced transcripts depends on SA and NPR1 in infected plants. Disruption of HDA19 leads to compromised resistance, whereas its overexpression results in enhanced resistance to P. syringae. Thus, HDA19 has a role opposite from those of WRKY38 and WRKY62 in basal resistance to the bacterial pathogen. Both WRKY38 and WRKY62 are transcriptional activators in plant cells, but their activation activities are abolished by overexpressed HDA19. Interaction of WRKY38 and WRKY62 with HDA19 may act to fine-tune plant basal defense responses.
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http://dx.doi.org/10.1105/tpc.107.055566DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2570728PMC
September 2008

Roles of Arabidopsis WRKY3 and WRKY4 transcription factors in plant responses to pathogens.

BMC Plant Biol 2008 Jun 20;8:68. Epub 2008 Jun 20.

Department of Botany and Plant Pathology, 915 W, State Street, Purdue University, West Lafayette, IN 47907-2054, USA.

Background: Plant WRKY DNA-binding transcription factors are involved in plant responses to biotic and abiotic responses. It has been previously shown that Arabidopsis WRKY3 and WRKY4, which encode two structurally similar WRKY transcription factors, are induced by pathogen infection and salicylic acid (SA). However, the role of the two WRKY transcription factors in plant disease resistance has not been directly analyzed.

Results: Both WRKY3 and WRKY4 are nuclear-localized and specifically recognize the TTGACC W-box sequences in vitro. Expression of WRKY3 and WRKY4 was induced rapidly by stress conditions generated by liquid infiltration or spraying. Stress-induced expression of WRKY4 was further elevated by pathogen infection and SA treatment. To determine directly their role in plant disease resistance, we have isolated T-DNA insertion mutants and generated transgenic overexpression lines for WRKY3 and WRKY4. Both the loss-of-function mutants and transgenic overexpression lines were examined for responses to the biotrophic bacterial pathogen Pseudomonas syringae and the necrotrophic fungal pathogen Botrytis cinerea. The wrky3 and wrky4 single and double mutants exhibited more severe disease symptoms and support higher fungal growth than wild-type plants after Botrytis infection. Although disruption of WRKY3 and WRKY4 did not have a major effect on plant response to P. syringae, overexpression of WRKY4 greatly enhanced plant susceptibility to the bacterial pathogen and suppressed pathogen-induced PR1 gene expression.

Conclusion: The nuclear localization and sequence-specific DNA-binding activity support that WRKY3 and WRKY4 function as transcription factors. Functional analysis based on T-DNA insertion mutants and transgenic overexpression lines indicates that WRKY3 and WRKY4 have a positive role in plant resistance to necrotrophic pathogens and WRKY4 has a negative effect on plant resistance to biotrophic pathogens.
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http://dx.doi.org/10.1186/1471-2229-8-68DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2464603PMC
June 2008

Genetic mapping of Pyrenophora teres f. teres genes conferring avirulence on barley.

Fungal Genet Biol 2007 May 16;44(5):323-9. Epub 2007 Jan 16.

Department of Plant Pathology, North Dakota State University, Fargo, ND 58105, USA.

A Pyrenophora teres f. teres cross between isolates 0-1 and 15A was used to evaluate the genetics of avirulence associated with barley lines Canadian Lake Shore (CLS), Tifang, and Prato. 15A is avirulent on Tifang and CLS, but virulent on Prato. Conversely, 0-1 is avirulent on Prato, but virulent on Tifang and CLS. Avirulence:virulence on Tifang and CLS segregated 1:1, whereas avirulence:virulence on Prato segregated 3:1. An AFLP-based linkage map was constructed and used to identify a single locus derived from 15A (AvrHar) conferring avirulence to Tifang and CLS. Virulence on Prato was conferred by two epistatic genes (AvrPra1 and AvrPra2). AvrPra2 co-segregated with AvrHar, but the two genes from opposite parents conferred opposite reactions. This work provides the foundation for the isolation of these avirulence genes.
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http://dx.doi.org/10.1016/j.fgb.2006.11.009DOI Listing
May 2007