Physical and Functional Interactions between Pathogen-Induced Arabidopsis WRKY18, WRKY40, and WRKY60 Transcription Factors

Abstract

Limited information is available about the roles of specific WRKY transcription factors in plant defense. We report physical and functional interactions between structurally related and pathogen-induced WRKY18, WRKY40, and WRKY60 transcription factors in Arabidopsis thaliana. The three WRKY proteins formed both homocomplexes and heterocomplexes and DNA binding activities were significantly shifted depending on which WRKY proteins were present in these complexes. Single WRKY mutants exhibited no or small alterations in response to the hemibiotrophic bacterial pathogen Pseudomonas syringae and the necrotrophic fungal pathogen Botrytis cinerea. However, wrky18 wrky40 and wrky18 wrky60 double mutants and the wrky18 wrky40 wrky60 triple mutant were substantially more resistant to P. syringae but more susceptible to B. cinerea than wild-type plants. Thus, the three WRKY proteins have partially redundant roles in plant responses to the two distinct types of pathogens, with WRKY18 playing a more important role than the other two. The contrasting responses of these WRKY mutants to the two pathogens correlated with opposite effects on pathogen-induced expression of salicylic acid-regulated PATHOGENESIS-RELATED1 and jasmonic acid-regulated PDF1.2. While constitutive expression of WRKY18 enhanced resistance to P. syringae, its coexpression with WRKY40 or WRKY60 made plants more susceptible to both P. syringae and B. cinerea. These results indicate that the three WRKY proteins interact both physically and functionally in a complex pattern of overlapping, antagonistic, and distinct roles in plant responses to different types of microbial pathogens.

The Role of WRKY Transcription Factors in Plant Immunity

“…Interestingly, Atwrky18 wrky40 double mutants also displayed enhanced resistance to the powdery mildew pathogen Golovonomyces orontii . In contrast, Atwrky18 wrky40 and Atwrky18 wrky60 double mutants were more susceptible to B. cinerea (Xu et al, 2006), and AtWRKY18 alone appears also to have positive regulatory functions in SAR . Dual functionality in defense signaling was also observed for AtWRKY53.…”

“…The closely related WRKY TFs AtWRKY18, -40, and -60 have partly redundant functions in negatively regulating resistance to P. syringae (Xu et al, 2006). Interestingly, Atwrky18 wrky40 double mutants also displayed enhanced resistance to the powdery mildew pathogen Golovonomyces orontii .…”

“…Upon herbivore attack, NaWRKY6 transcript accumulation was shown to be dependent on NaWRKY3 expression (Skibbe et al, 2008). Moreover, physical interaction of related WRKY TFs may also be necessary for their efficient function, as evidenced by homodimer and heterodimer complex formation of Arabidopsis WRKY18, -40, and -60 in response to P. syringae (Xu et al, 2006).…”

A systems biology perspective on the role of WRKY transcription factors in drought responses in plants

“…First, there is now considerable evidence that wRKY transcription factors form homo-and hetero-complexes. This includes interaction of group IIa wRKY proteins with each other via leucine zipper motifs (Cormack et al 2002;Xu et al 2006), interaction of group III wRKY TFs (Besseau et al 2012) and heterodimerization of members of group IIb. In addition, there are reports of heterodimerization of wRKY TFs from different subfamilies such as OswRKY71 and OswRKY51 (groups IIa and IId, respectively) (Xie et al 2006) and the group IIa TFs AtwRKY40 and AtwRKY60 interact with AtwRKY36 (IId) and AtwRKY38 (III) (Arabidopsis Interactome Mapping Consortium (2011)).…”

Expression analysis ofWRKYgenes fromPoncirus trifoliatain response to pathogen infection

“…WRKY33, WRKY40 and WRKY60 from Arabidopsis (Asai et al 2002;Zheng et al 2006;Xu et al 2006;Zheng et al 2007;Lai et al 2008), TIZZ from tobacco (Yoda et al 2002), CaWRKY-a and CaWRKY2 (Oh et al 2006) from pepper, and VvWRKY1 and VvWRKY2 from grapevine ) are induced in response to pathogen infections. The involvement of some of the WRKY genes in plant defense and resistance to specific pathogens was experimentally demonstrated, suggesting that the PtrWRKY1 gene induced in response to CTV infection and the PtrWRKY3 gene induced in response to P. citrophthora infection may contribute resistance to these pathogens in Poncirus.…”