A barley protein kinase positively regulates disease resistance through mediating phosphorylation-coupled turnover of a defense repressor WRKY3
L. ZHANG (1), X. Han (1), P. Xue (1), Q. Shen (1) (1) Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, China

Upon recognition of pathogens, plant immune receptors trigger immune responses that usually involving massive defense transcription reprogramming. Although numerous transcription factors (TFs) were identified to regulate plant defense, the components and mechanisms controlling these TFs are largely unknown. We have identified three barley TFs, WRKY1, WRKY2 and WRKY3, acting as repressors in basal and race-specific immunity against the powdery mildew fungus. We report here that a barley protein kinase SnRK1 specifically interacts with WRKY3 and regulates its stability and activity. SnRK1 interaction with WRKY3 was shown by yeast two-hybrid and in vitro pull-down assays. Bimolecular fluorescence complementation (BiFC) analysis confirmed that they interact in plant nucleus. Phospho-protein mobility shift assays demonstrated that activated SnRK1 can phosphorylate WRKY3 in vitro at residue serine 112, which resides in a conserved SnRK1-targeting motif. Moreover, SnRK1 activation resulted in WRKY3 phosphorylation and promoted its proteasomal degradation in Nicotiana benthamiana. The phosphorylation-null mutant WRKY3S112A was resistant to proteasomal degradation. WRKY3 wild-type and WRKY3S112A acted as a transcription repressor and activator in protoplast assays, respectively. Overexpression of SnRK1 in barley derepressed WRKY3 regulated defense responses and enhanced disease resistance to the powdery mildew fungus. Our results suggest SnRK1 acts upstream of WRKY3 and activates defense responses through phosphorylation-coupled degradation of WRKY3.

Abstract Number: P17-647
Session Type: Poster