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

Abstract

Reactive oxygen species (ROS) and salicylic acid (SA) are two factors regulating leaf senescence and defense against pathogens. However, how a single gene integrates both ROS and SA pathways remains poorly understood. Here, we show that <i>Arabidopsis</i> WRKY55 transcription factor positively regulates ROS and SA accumulation, and thus leaf senescence and resistance against the bacterial pathogen <i>Pseudomonas syringae</i><i>WRKY55</i> is predominantly expressed in senescent leaves and encodes a transcriptional activator localized to nuclei. Both inducible and constitutive overexpression of <i>WRKY55</i> accelerates leaf senescence, whereas mutants delay it. Transcriptomic sequencing identified 1448 differentially expressed genes, of which 1157 genes are upregulated by <i>WRKY55</i> expression. Accordingly, the ROS and SA contents in <i>WRKY55</i>-overexpressing plants are higher than those in control plants, whereas the opposite occurs in mutants. Moreover, WRKY55 positively regulates defense against <i>P. syringae</i> Finally, we show that WRKY55 activates the expression of <i>RbohD</i>, <i>ICS1</i>, <i>PBS3</i> and <i>SAG13</i> by binding directly to the W-box-containing fragments. Taken together, our work has identified a new WRKY transcription factor that integrates both ROS and SA pathways to regulate leaf senescence and pathogen resistance.