[<i>Gm</i>WRKY33A positively regulates disease resistance in soybean (<i>Glycine max</i>)].

The WRKY transcription factor gene family is a plant-specific transcription factor that plays important roles defense responses. Studies in model plant <i>Arabidopsis</i> demonstrated that WRKYs function downstream of mitogen activated-protein kinase (MAPK) signaling cascade and participate in defense responses through activating the expression of defense-related genes. However, the roles of WRKYs in defense responses have not been previously investigated in paleopolyploidy soybean. Bioinfomatic analysis revealed that there are three pair of <i>GmWRKY33</i> genes in the soybean genome. The identity of first two pair of GmWRKY33 genes is greater than 84% (named as <i>GmWRKY33A</i>). The identity of genes within the same pair is greater than 95%. A 300 bp fragment highly homologous to these four <i>GmWRKY33A</i> was chosen to clone into bean pod mosaic virus (BPMV)-based silencing vector (BPMV-VIGS) to achieve the goal of silencing four <i>GmWRKY33A</i> genes simultaneously. In this study, we simultaneously silenced four homologous genes of <i>GmWRKY33A</i> using a bean pod mottle virus (BPMV) vector carrying a single fragment of <i>GmWRKY33A</i>. Comparing the silenced plants with the vector control plants, no evident morphological phenotypes were observed. However, the <i>GmWRKY33A-</i>silenced plants exhibited significantly reduced resistance to <i>Pseudomonas syringae</i> pv. <i>glycinea</i> (<i>Psg</i>), <i>Xanthomonas axonopodis</i> pv. <i>glycine</i> (<i>Xag</i>), as well as to soybean mosaic virus (SMV). Furthermore, we demonstrated that silencing these <i>GmWRKY33A</i> genes significantly inhibited the activation of <i>Gm</i>MPK3/<i>Gm</i>MPK6 induced by <i>Psg</i> infection. Collectively, our results suggest that <i>Gm</i>WRKY33As are involved in soybean immunity through regulating the transcription of <i>GmMPK3/6</i> genes or activating the kinase activities of <i>Gm</i>MPK3/6. Taken together, our results demonstrated that <i>Gm</i>WRKY33As are positive regulators of soybean immune responses.