Progress 10/01/07 to 09/30/13
Outputs
Target Audience: The target audiences for the knowledge generated from the project include scientists worldwide in the field of plant molecular biology working in research universities, institutes and industrial companies. In addition, the project provides training for undergraduate, and graduate students and other research scientists. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? One research scientist, six graduate students and three undergraduate students are involved in the projects and received training and professional development from the projects. They are: Baofang Fan: research scientist, Zuyu Zheng : Graduate student Zhenhua Luo: Graduate student Yuan Cheng: Graduate student Jie Zhou: Graduate student Heather Clover: Undergraduate student Fei Sun: Undergraduate student How have the results been disseminated to communities of interest? The results have been disseminated to scientific communities through publications in scientific journals and progress reports to USDA. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
The overall goal of the project is to understand the molecular mechanisms of two important Arabidopsis WRKY proteins, WRKY18 and WRKY33, in plant innate immune responses by investigating their interacting partners and target genes under their regulation during plant-pathogen interactions. Over the last five years, we have established that WRKY18 interacts with WRKY40 and WRKY60 both physically and functionally in a complex manner of overlapping, antagonistic and distinct roles not only in plant responses to different types of microbial pathogens. Furthermore, we have found that the three WRKYs are also involved in plant responses to abscisic acid (ABA) and abiotic stress. 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. Thus, the three related WRKY transcription factors form a highly interacting regulatory network that modulates gene expression in both plant defense and stress responses. Our studies on WRKY33 have provided important results on plant resistance to necrotrophic pathogens, an important but understudied group of plant pathogens. Major accomplishments from these studies include functional analysis of two types of WRKY33-interacting proteins. We have shown that WRKY33 physically interacts interaction with two VQ motif-containing proteins, SIB1 and SIB2, in plant cells. Both SIB1 and SIB2 acts as activators of WRKY33 by recognizing the WRKY DNA-binding domain of WRKY33 and stimulating its sequence-specific DNA-binding activity. By searching the Arabidopsis genome, we have identified 34 genes encoding VQ motif-containing proteins. We have conducted a comprehensive structural and functional analysis of the newly identified gene family and provided important evidence for their critical roles in plant growth, development and responses to environmental cues. We have also found that WRKY33 interacts with ATG18a, a critical autophagy protein in Arabidopsis. 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. Arabidopsis mutants defective in autophagy exhibit enhanced susceptibility to the necrotrophic fungal pathogens B. cinerea and Alternaria brassicicola. These results strongly suggest that autophagy cooperates with jasmonate- and WRKY33-mediated signaling pathways in the regulation of plant defense responses to necrotrophic pathogens. We collaborated with Dr. Shuqun Zhang’s group at University of Missouri in the studies of the regulation and target genes of WRKY33. Plant sensing of invading pathogens triggers the induction of secondary antimicrobial compounds known as phytoalexins. MPK3 and MPK6, two pathogen-responsive mitogen-activated protein kinases, play essential roles in the induction of camalexin, the major phytoalexin in Arabidopsis. We have found that WRKY33 is required for MPK3/MPK6-induced camalexin biosynthesis. In wrky33 mutants, both gain-of-function MPK3/MPK6- and pathogen-induced camalexin production are compromised. WRKY33 is a pathogen-inducible transcription factor, whose expression is regulated by the MPK3/MPK6 cascade. Furthermore, WRKY33 is a substrate of MPK3/MPK6. Mutation of MPK3/MPK6 phosphorylation sites in WRKY33 compromises its ability to complement the camalexin induction in the wrky33 mutant. Based on these data, we conclude that WRKY33 functions downstream of MPK3/MPK6 in reprogramming the expression of camalexin biosynthetic genes.
Publications
- Type:
Journal Articles
Status:
Accepted
Year Published:
2014
Citation:
Zhou, J., Zhang, Y., Qi, J., Chi, Y., Fan, B., Yu, J.-Q., Chen, Z. (2013). E3 ubiquitin ligase CHIP and NBR1-mediated selective autophagy protect additively against proteotoxicity in plant stress responses. Plos Genetics (in press)
|
Progress 10/01/11 to 09/30/12
Outputs
OUTPUTS: The overall objectives of the project include identification and functional analysis of pathogen-induced Arabidopsis WRKY genes, their interacting proteins and target genes in plant defense and stress responses. Arabidopsis WRKY33 transcription factor plays a critical role in plant resistance to necrotrophic pathogens. We have shown that WRKY33 physically interacts interaction with two VQ motif-containing proteins, SIB1 and SIB2, in plant cells. Both SIB1 and SIB2 acts as activators of WRKY33 by recognizing the WRKY DNA-binding domain of WRKY33 and stimulating its sequence-specific DNA-binding activity. By searching the Arabidopsis genome, we have identified 34 genes encoding VQ motif-containing proteins. We have conducted a comprehensive structural and functional analysis of the newly identified gene family and provided important evidence for their critical roles in plant growth, development and responses to environmental cues. In collaboration with Dr. Jing-Quan Yu's group at Zhejiang University in China, we have also established that cellular glutathione redox homostasis plays a critical role in induced CO2 assimilation by plant hormone brassinosteroids. Some of the results from these research activities have been published in three papers in scientific journals. In addition, two graduate students, one research scientist and three visiting scientists participated in the projects and received research experience and mentoring. PARTICIPANTS: Zhixiang Chen, project director Fei Wang, graduate student Zhe Wang, graduate student Baofang Fam, research scientist Yuan Chen, visiting scientist Fei Sun, visiting scientist Jie Zhou, visiting scientist TARGET AUDIENCES: The target audiences for the knowledge generated from the project include scientists worldwide in the field of plant molecular biology working in research universities, institutes and industrial companies. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
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. Two WRKY33-interacting proteins, nuclear-encoded SIB1 and SIB2, also interact with plastid-encoded plastid RNA polymerase SIGMA FACTOR1, 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. Over the last year, we have analyzed the entire family of 34 structurally divergent VQ proteins from Arabidopsis. Arabidopsis VQ proteins interacted specifically with the C-terminal WRKY domains of group I and the sole WRKY domains of group IIc WRKY proteins. Using site-directed mutagenesis, we identified structural features of these two closely related groups of WRKY domains that are critical for interaction with VQ proteins. Expression of a majority of Arabidopsis VQ genes was responsive to pathogen infection and salicylic acid treatment. Functional analysis using both knockout mutants and overexpression lines revealed strong phenotypes in growth, development, and susceptibility to pathogen infection. Altered phenotypes were substantially enhanced through cooverexpression of genes encoding interacting VQ and WRKY proteins. These findings indicate that VQ proteins play an important role in plant growth, development, and response to environmental conditions, most likely by acting as cofactors of group I and IIc WRKY transcription factors. Brassinosteroids (BRs) play a vital role in plant growth, stress tolerance and productivity. The involvement of BRs in the regulation of CO2 assimilation and cellular redox homeostasis has been studied. Exogenous BR increased apoplastic H2O2 accumulation, the ratio of reduced to oxidized glutathione (GSH:GSSG) and CO2 assimilation, whereas a BR biosynthetic inhibitor had the opposite effects. BR-induced CO2 assimilation was decreased by a H2O2 scavenger or inhibition of H2O2 generation, GSH biosynthesis and the NADPH-generating pentose phosphate pathway. BR-, H2O2 - or GSH-induced CO2 assimilation was associated with increased activity of enzymes in the Benson-Calvin cycle. BR increased the content of RCA and this effect was blocked by inhibitors of redox homeostasis. These results strongly suggest that BR-induced photosynthesis involves an H2O2 -mediated increase in the GSH:GSSG ratio, which may positively regulate the synthesis and activation of redox-sensitive enzymes in carbon fixation.
Publications
- Lai, Z. Li, Y., Wang, F., Cheng, Y., Fan, B., Yu, J.-Q.and Chen, Z. (2011) Arabidopsis sigma factor-binding proteins are coactivators of WRKY33 transcription factor in defense against necrotrophic pathogens. Plant Cell 23:3824-3841.
- Jiang Y.-P., Cheng F., Zhou, Y.-H., Xia, X.-J., Mao, W.-H., Shi, K., Chen, Z., Yu, J.-Q. (2012) Cellular glutathione redox homeostasis plays an important role in brassinosteroid-induced increase in CO2 assimilation in Cucumis sativus. New Phytol. 194:932-943.
- Cheng, Y., Zhou, Y., Yang, Y., Chi, Y.-J., Zhou, J., Chen, J.-Y., Wang, F., Fan, B., Shi, K., Zhou, Y.-H., Yu, J.-Q., Chen, Z. (2012) Structural and functional analysis of VQ motif-containing proteins in Arabidopsis and soybean as WRKY-interacting proteins. Plant Physiol. 159: 810-825.
|
Progress 10/01/10 to 09/30/11
Outputs
OUTPUTS: The overall objectives of the project include identification and functional analysis of pathogen-induced Arabidopsis WRKY genes, their interacting proteins and target genes in plant defense. In collaboration with Dr. Shuqun Zhang's group at University of Missouri, we have also established that phosphorylation of WRKY33 by pathogen-responsive mitogen-activated protein kinase 3 and 6 is important for phytoalexin biosynthesis in Arabidopsis. We have shown that the important role of WRKY33 in plant defense is in part mediated by its role in the regulation of plant autophagy and we have established that plant autophagy is critical for plant defense to necrotrophic pathogens. In addition to their roles in plant biotic stress responses, we have recently found that Arabidopsis WRKY18, 40 and 60 transcription factors are involved in plant responses to abscisic acid and abiotic stress. Some of the results from these research activities have been published in five papers in scientific journals. In addition, one graduate student, one research scientist and two visiting scientists participated in the project and received research experience and mentoring. PARTICIPANTS: Fei, Wang, graduate student, Purdue University. Baofang Fan, research scientist, Purdue University. Yuan Cheng, visiting scholar, Zhejiang University, China. Jie Zhou, visiting scientist, Zhejiang University Dr. Shuqun Zhang, collaborator from University of Missouri. TARGET AUDIENCES: Scientists from universities, government agencies and biotech companies with interest in plant biology, crop sciences, plant pathology and biotechnology. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Plant sensing of invading pathogens triggers the induction of secondary antimicrobial compounds known as phytoalexins. MPK3 and MPK6, two pathogen-responsive mitogen-activated protein kinases, play essential roles in the induction of camalexin, the major phytoalexin in Arabidopsis. We have found that WRKY33 is required for MPK3/MPK6-induced camalexin biosynthesis. In wrky33 mutants, both gain-of-function MPK3/MPK6- and pathogen-induced camalexin production are compromised. WRKY33 is a pathogen-inducible transcription factor, whose expression is regulated by the MPK3/MPK6 cascade. Furthermore, WRKY33 is a substrate of MPK3/MPK6. Mutation of MPK3/MPK6 phosphorylation sites in WRKY33 compromises its ability to complement the camalexin induction in the wrky33 mutant. Based on these data, we conclude that WRKY33 functions downstream of MPK3/MPK6 in reprogramming the expression of camalexin biosynthetic genes. Autophagy is a pathway for degradation of cytoplasmic components. We have found 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. Arabidopsis mutants defective in autophagy exhibit enhanced susceptibility to the necrotrophic fungal pathogens B. cinerea and Alternaria brassicicola. These results strongly suggest that autophagy cooperates with jasmonate- and WRKY33-mediated signaling pathways in the regulation of plant defense responses to necrotrophic pathogens. Arabidopsis WRKY18, 40, and 60 transcription factors interact both physically and functionally in plant defense. We have found that the three WRKYs are also involved in plant responses to abscisic acid (ABA) and abiotic stress. 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. Thus, the three related WRKY transcription factors form a highly interacting regulatory network that modulates gene expression in both plant defense and stress responses.
Publications
- Chen, H., Lai, Z., Shi, J., Xiao, Y., Chen, Z., Xu, X. (2010) Roles of Arabidopsis WRKY18, WRKY40 and WRKY60 transcription factors in plant responses to abscisic acid and abiotic stress. BMC Plant Biology 10:281
- Cui, J.-X., Zhou, Y.-H., Ding, J.-G., Xia, X.-J., Shi, K., Chen, S.-C., Asami, T., Chen, Z., and Yu, J.-Q. (2011) Role of nitric oxide in hydrogen peroxide-dependent induction of abiotic stress tolerance by brassinosteroids in cucumber. Plant, Cell and Environ. 34:347-358.
- Lai, Z. Wang, F., Zheng, Z., Fan, B., and Chen, Z. (2011) A critical role of autophagy in plant resistance to necrotrophic fungal pathogens in Arabidopsis. Plant J. 66:953-968.
- Mao, G., Meng, X., Liu, Y., Zheng, Z., Chen, Z., and Zhang, S. (2011) Phosphorylation of a WRKY transcription factor by two pathogen-responsive MAPKs drives phytoalexin biosynthesis in Arabidopsis. Plant Cell 23:1639-1653.
- Xia, X.-J., Zhou, Y.-H., Ding, J., Shi, K., Asami, T., Chen, Z., and Yu, J.-Q. (2011) Induction of systemic stress tolerance by brassinosteroid in Cucumis sativus. New Phytologist 191:706-760.
|
Progress 10/01/09 to 09/30/10
Outputs
OUTPUTS: The overall objectives of the project include identification and functional analysis of pathogen-induced Arabidopsis WRKY genes, their interacting proteins and target genes in plant defense. Over the past year, we have been continuing our studies on Arabidopsis WRKY33 important for plant resistance to necrotrophic fungal pathogens. We have identified and functionally analyzed two interacting proteins for WRKY33 and demonstrated that they are activators of WRKY33 with an important role in WRKY33-mediated disease resistance. During our studies of plant defense responses, we have previously identified an Arabidopsis mutant (eps1) that exhibits enhanced susceptibility to the bacterial pathogen Pseudomonas syringae. We have cloned the gene and found it encoding an acetyl CoA transferase and proposed that the enzyme is involved in salicylic acid (SA) biosynthesis. The involvement of an acetyl CoA transferase in SA biosynthesis raises the possibility that SA biosynthetic pathway might be more complicated than previously thought. To analyze the involvement of phenylalanine ammonia lyases (PALs) in SA biosynthesis, we have functionally analyze the four PAL genes from Arabidopsis. Some of the results from these research activities have been published in two papers in scientific journals. In addition, two graduate students and one research scientist participated in the project and received research experience and mentoring. PARTICIPANTS: Two graduate students (Zhibing Lai and Fei Wang) and one research scientist (Baofang Fan) received research experience and mentoring. TARGET AUDIENCES: Target audiences include students and scientists working in the general fields of biology, particularly in plant biology and plant pathology, in universities and biotechnology companies. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Phenylalanine ammonia-lyase (PAL) catalyzes the first step of the phenylpropanoid pathway, which produces precursors to a variety of important secondary metabolites. Arabidopsis contains four PAL genes (PAL1 to PAL4) but there has been no genetic analysis to assess the biological functions of the entire gene family. We have generated and analyzed combined mutations for the four Arabidopsis PAL genes. 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. Thus, PAL1 and PAL2 have a redundant role in flavonoid biosynthesis. Furthermore, the pal1 pal2 double mutants were more sensitive to UV-B 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. 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. Necrotrophic pathogens are an important group of plant pathogens that cause many devastating plant diseases. WRKY33 transcription factor is important for plant resistance to necrotrophic pathogens and, therefore, elucidation of its functions will help our understanding of plant immune system against this important type of pathogens. We have identified and functionally analyzed two WRKY33-interacting proteins in WRKY33-mediated plant defense. Using yeast two-hybrid screens, we have discovered that WRKY33 binds two nuclear-encoded proteins. The two WRKY33-interacting contain a N-terminal chloroplast targeting signal and a putative nuclear localization signal, suggesting that they are dual-targeted to both chloroplasts and the nucleus. Bimolecular fluorescence complementation indicates that WRKY33 interacts with the two proteins in the nucleus of plant cells. The two WRKY33-interacting proteins stimulated the DNA-binding activity of WRKY33. Like WRKY33, genes encoding the WRKY33-interacting proteins are rapidly and strongly induced by necrotrophic pathogens. Resistance to necrotrophic pathogens is compromised in the mutants but enhanced in the transgenic plants overexpressing the genes encoding the WRKY33-interacting proteins. These results strongly suggest that dual-targeted WRKY33-interacting proteins function as activators of WRKY33 in plant defense against necrotrophic pathogens.
Publications
- Xia, X.-J., Chen, Z., Yu, J.-Q. (2010) ROS mediate brassinosteroids-induced plant stress responses. Plant Signaling & Behavior 5:532-534.
- Huang, J., Gu, M., Lai, Z., Fan, B., Shi, K., Zhou, Y.-H., Yu, J.-Q., and Chen, Z. (2010) Functional analysis of the Arabidopsis PAL gene family in plant growth, development and response to environmental stress. Plant Physiol. 153:1526-1538.
|
Progress 10/01/08 to 09/30/09
Outputs
OUTPUTS: The overall objectives of the project include identification and functional analysis of pathogen-induced Arabidopsis WRKY genes, their interacting proteins and target genes in plant defense. Over the past year, we have been focusing on Arabidopsis WRKY33 important for plant resistance to necrotrophic fungal pathogens. We have also identified two interacting proteins for WRKY33 and demonstrated that they are coactivators of WRKY33 with an important role in plant disease resistance. During our studies of plant WRKY genes, we have identified an Arabidopsis mutant (eps1) that exhibits enhanced susceptibility to the bacterial pathogen Pseudomonas syringae. We have determined that the susceptible phenotype of the eps1 mutant is due to compromised accumulation of plant defense signal molecule salicylic acid. We have also cloned the gene and found it encoding an acetyl CoA transferase and proposed that the enzyme is involved in salicylic acid biosynthesis. Some of the results from these research activities have been published in two papers in scientific journals. In addition, two graduate students and one research scientist participated in the project and received research experience and mentoring. PARTICIPANTS: Two graduate students (Zuyu Zheng and Zhibing Lai) and one research scientist (Baofang Fan) participated in the project and received research training and mentoring. TARGET AUDIENCES: One of the graduate student participating in the project, Zhibing Lai, attended an international Plant-Microbe Interaction conference in Montreal, Canada and presented an poster on his research on WRYK33 and its interacting proteins. Zhixiang Chen, the project PI, gave invited seminars on the project at three University in China (Zhejiang University, Zhejiang University of Technology and Sciences and Zhongshan University). PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Salicylic acid is an important regulator of plant resistance to biotrophic and hemibiotrophic pathogens. The enhanced pseudomonas susceptibility 1 (eps1) mutant in Arabidopsis thaliana is hypersusceptible to both virulent and avirulent strains of the bacterial pathogen Pseudomonas syringae. Through positional cloning, the EPS1 gene was isolated and found to encode a novel member of the BAHD acyltransferase superfamily. Pathogen-induced accumulation of salicylic acid and expression of Pathogenesis-related (PR) genes were compromised in the esp1 mutant. Salicylic acid could induce PR1 gene expression and restore disease resistance in the esp1 mutant. These results suggest that EPS1 functions upstream of salicylic acid and may be involved directly in the synthesis of a precursor or a regulatory molecule for salicylic acid biosynthesis. Mutations of EPS1 or other genes important for salicylic acid accumulation or signaling conferred enhanced resistance to necrotrophic fungal pathogens Botrytis cinerea and Alternaria brassicicola in the Nossen-0 background but had little effect in the Columbia-0 background. These results suggest that there is natural variation among Arabidopsis ecotypes in the antagonistic crosstalk between defense signaling pathways against different types of microbial pathogens. The Arabidopsis thaliana WRKY33 transcription factor is important for plant resistance to necrotrophic pathogens. Over the past year, we have identified new WRKY33-interacting proteins and determined their roles in the activation of WRKY33 and plant defense. Using yeast two-hybrid screens, we have discovered that WRKY33 binds nuclear-encoded SIB1 and SIB2, which also interact with plastid-encoded plastid RNA polymerase sigma-factor Sig1. Both SIB1 and SIB2 contain a N-terminal chloroplast targeting signal peptide and a cluster of basic amino acid residues characteristic of nuclear localization signals, suggesting that the two proteins are dual-targeted to both chloroplasts and the nucleus. Bimolecular fluorescence complementation indicates that WRKY33 interacts with SIBs in the nucleus of plant cells. Like previously identified MKS1, the two SIB proteins contain a short QV motif that is important for interaction with WRKY33. The SIB-interacting domain of WRKY33 has been mapped to the C-terminal WRKY domain, which is known to be responsible for sequence-specific binding to DNA. SIB proteins stimulate the DNA-binding activity of WRKY33 but have little effect on its transcription regulatory activity. Like WRKY33, both SIB1 and SIB2 are rapidly and strongly induced by necrotrophic pathogens. Resistance to necrotrophic pathogens is compromised in the sib1 and sib2 mutants and is enhanced in the transgenic plants overexpressing SIB1. These results strongly suggest that dual-targeted SIBs function as coactivators of WRKY33 transcription factor in defense against necrotrophic pathogens
Publications
- Zheng, Z., Qualley, A., Fan, B., Dudareva, N., and Chen, Z. (2009) An important role of a novel BAHD acyl transferase-like protein in plant innate immunity. Plant J. 57:1040-1053.
- Chen, Z., Zheng, Z., Huang, J., Lai, Z., and Fan, B. (2009) Biosynthesis of salicylic acid in plants. Plant Signaling & Behavior 4:493-496.
|
Progress 10/01/07 to 09/30/08
Outputs
OUTPUTS: The overall objectives of the project include identification and functional analysis of a number of pathogen-induced Arabidopsis WRKY genes, their interacting proteins and target genes in plant defense. Over the past years, we have established the biological functions of five pathogen-induced Arabidopsis WRKY genes (WRKY3, WRKY4, WRKY38, WRKY48 and WRKY62). We have also identified and functionally analyzed interacting proteins for WRKY33, WRKY38 and WRKY62. Some of the results from these research activities have been published in three papers in scientific journals. In addition, one postdoctoral fellow and two graduate students participated in the project and received research experience and mentoring. PARTICIPANTS: Kang-chang Kim, postdoctoral fellow. Zuyu Zheng, graduate student. Zhibing Lai, graduate student. TARGET AUDIENCES: The scientific community in the studies of molecular basis of plant disease resistance PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Arabidopsis WRKY3 and WRKY4 genes encode two structurally similar WRKY proteins and are induced by pathogen infection. Both WRKY3 and WRKY4 are nuclear-localized and specifically recognize the TTGACC W-box sequences. We have isolated mutants and generated overexpression lines and examined them for responses to the biotrophic bacterial pathogen Pseudomonas syringae and 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. These results indicate 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. Arabidopsis WRKY48 is also induced by pathogen infection. Growth of a virulent strain of the bacterial pathogen Pseudomonas syringae was decreased in the wrky48 T-DNA insertion mutants. The enhanced resistance of the loss-of-function mutants was associated with increased induction of salicylic acid-regulated PR1 by the bacterial pathogen. By contrast, transgenic WRKY48-overexpressing plants support enhanced growth of P. syringae and the enhanced susceptibility was associated with reduced expression of defense-related PR genes. Therefore, WRKY48 is a negative regulator of PR gene expression and basal resistance to the bacterial pathogen P. syringae. Arabidopsis WRKY38 and WRKY62, encoding two structurally similar WRKY proteins, are induced by salicylic acid. Disease resistance was enhanced in the wrky38 and wrky62 single mutants and, to a greater extent, in the wrky38 wrky62 double mutants. By contrast, overexpression of WRKY38 or WRKY62 reduced disease resistance and PR1 expression. Thus WRKY38 and WRKY62 function additively as negative regulators of plant basal defense. WRKY38 and WRKY62 interact with HDA19, a histone deacetylase. Disruption of HDA19 led 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 plant basal resistance to the bacterial pathogen. Both WRKY38 and WRKY62 are transcriptional activators in plant cells but their transcriptional activation activities are abolished by overexpressed HDA19. The functional interactions of WRKY38 and WRKY62 with HDA19 through physical interactions may function for fine-tuning of plant defense. Our studies have provided direct evidence that pathogen-induced plant WRKY proteins have regulatory roles in plant defense against different types of microbial pathogens. In addition, we have started to address the specific molecular mechanisms by which plant WRKY proteins regulate plant defense responses and disease resistance. Our studies could lead to identification of specific molecular mechanisms and specific plant genes that could be exploited for genetic engineering of disease resistance in crop plants.
Publications
- Xing, D., Lai, Z., Zheng, Z., Fan, B., and Chen (2008) Stress- and pathogen-induced Arabidopsis WRKY48 is a transcriptional activator that represses plant basal defense. Mol. Plant 1:459-470.
- Zhibing Lai, K. M. Vinod., Zuyu Zheng, Baofang Fan and Zhixiang Chen (2008) Role of Arabidopsis WRKY3 and WRKY4 transcription factors in plant responses to pathogens. BMC Plant Biology 8:68.
- Kang, C., Lai, Z., Fan, B., and Chen, Z. (2008) Arabidopsis WRKY38 and WRKY62 transcription factors interact with histone deacetylase 19 in basal defense. Plant Cell 20:2357-2371.
|
|