Fine-tuning of the dual-role transcription factor WRKY8 via differential phosphorylation for robust broad-spectrum plant immunity.

Abstract

Plants utilize plasma membrane-localized pattern recognition receptors (PRRs) to perceive pathogen-associated molecular patterns (PAMPs) to activate broad-spectrum pattern-triggered immunity (PTI). However, the regulatory mechanism ensuring robust broad-spectrum plant immunity remains largely unknown. Here, we reveal the dual roles of the transcription factor WRKY8 in transcriptional regulation of PRR genes: repressing the nlp20/nlp24 receptor gene RLP23 whereas promoting the chitin receptor gene CERK1. Remarkably, SsNLP1 and SsNLP2, two nlp24 type PAMPs in the destructive fungal pathogen Sclerotinia sclerotiorum, activate two calcium-elicited kinases, CPK4 and CPK11 to phosphorylate WRKY8 and consequently release its inhibition on RLP23 expression to accumulate RLP23. Meanwhile, SsNLPs activate a RLCK type kinase, PBL19 to phosphorylate WRKY8 and consequently enhance the accumulation of CERK1. Intriguingly, RLP23 is repressed at late stage by PBL19-mediated phosphorylation of WRKY8, to avoid excessive immunity for normal growth. Our findings unveil a "killing two birds with one stone" strategy employed by plants to elicit robust broad-spectrum immunity, which is based on PAMP-triggered fine-tuning of a dual-role transcription factor to simultaneously amplify two PRRs recognizing PAMPs well conserved in a wide range of pathogens. Moreover, our results reveal a novel plant strategy based on fine-tuning of multiple PRR gene expression to balance the trade-off between growth and immunity.