WRKY55 transcription factor positively regulates leaf senescence and defense response through modulating the transcription of genes implicated in ROS and SA biosynthesis in Arabidopsis

Reactive oxygen species (ROS) and salicylic acid (SA) are two factors regulating leaf senescence and pathogen defense. However, how a single gene integrates both ROS and SA pathways remains poorly understood. Here, we show that Arabidopsis WRKY55 transcription factor positively regulates ROS and SA accumulation and thus leaf senescence and resistance against the bacterial pathogen Pseudomonas syringae. WRKY55 is predominantly expressed in senescent leaves and encodes a transcriptional activator localized to nuclei. Both inducible and constitutive overexpression of WRKY55 accelerates leaf senescence, while mutants delay it. A transcriptomic sequencing identified 1,448 differentially expressed gens (DEGs), of which 1,157 genes are up-regulated by WRKY55 expression. Accordingly, the ROS and SA contents in WRKY55-overexpression plants are higher than that in the control, while mutants showed a contrast change. Moreover, WRKY55 positively regulates defense against Pseudomonas syringae. Finally we show that WRKY55 activates the expression of RbohD, ICS1, PBS3 and SAG13 through directly binding to the W-box-containing fragments. Taken together, our work has identified a novel WRKY transcription factor that integrates both ROS and SA pathways to regulate leaf senescence and pathogen resistance.