Although numerous advances have been made in understanding the mechanisms of WRKY transcription factors in defense against Botrytis cinerea, the specific mechanisms by which different WRKY transcription factors cooperate or oppose each other are not well understood.

Prof. YU Diqiu’s team of Xishuangbanna Tropical Botanical Garden (XTBG) has focused on studying functions of WRKY 57, Group IIc of WRKY transcription factor family. Their previous research confirmed that transcription factor Arabidopsis thaliana WRKY57 was involved in jasmonate(JA)-induced leaf senescence. In a recent study, they reported the identification and functional analysis of WRKY57 in compromising plant defense against the necrotrophic pathogen B. cinerea.

The researchers firstly checked the expression levels of WRKY57 upon challenge with Botrytis cinerea, a necrotrophic fungus that caused gray mold disease in many plant species. They aimed to investigate whether WRKY57 was involved in JA-related defense against necrotrophic fungi. Expression of WRKY57 was moderately induced by B. cinerea treatment. They also checked the expression levels of WRKY57 upon Pst DC3000 treatment and found that expression of WRKY57 was induced rapidly by Pst DC3000 at 3 h. They speculated that WRKY57 may function in the basal defense process in Arabidopsis.

By further analysis, the researchers found that loss of WRKY57 function enhanced basal defense against B. cinerea and WRKY57’s negative regulation of defense was related to JA signaling pathway. By chromatin immunoprecipitation (ChIP), JASMONATE ZIM-DOMAIN 1 (JAZ1) and JAZ5, direct targets of WRKY33, were identified as direct target genes of WRKY57 in vivo. Using the yeast two-hybrid assay, they revealed that WRKY57 interacted with two VQ motif-containing proteins, SIB1 and SIB2, which also interacted with WRKY33. They also found that the Zinc-finger-motif and VQ-motif were important for the interaction of WRKY57 and SIB1 and SIB2.Furthermore, transient transcriptional activity assays showed that WRKY57 and WRKY33 competitively regulated JAZ1 and JAZ5, and SIB1 and SIB2 further enhanced those competitions of WRKY57 to WRKY33.

The results demonstrated that WRKY57 negatively regulated resistance of Arabidopsis against B. cinerea. The negative role of AtWRKY57 in B. cinerea infection was mainly resulting from that WRKY57 and WRKY33 competitively interacted with SIB1 and SIB2 and then WRKY57 competed with WRKY33 to regulate its downstream target JAZ1 and JAZ5 genes.

The study entitled “WRKY57 regulates JAZ genes transcriptionally to compromise Botrytis cinerea resistance in Arabidopsis thaliana” has been published online in Plant Physiology.