WRKY42 transcription factor positively regulates leaf senescence through modulating SA and ROS synthesis in Arabidopsis thaliana

Leaf senescence represents the final stage of leaf growth and development, and its onset and progression are strictly regulated; however, the underlying regulatory mechanisms remain largely unknown. In this study we found thatWRKY42was highly induced during leaf senescence. Loss-of-functionwrky42mutants showed delayed leaf senescence whereas the overexpression ofWRKY42accelerated senescence. Transcriptome analysis revealed 2721 differentially expressed genes between wild-type andWRKY42-overexpressing plants, including genes involved in salicylic acid (SA) and reactive oxygen species (ROS) synthesis as well as several senescence-associated genes (SAGs). Moreover, WRKY42 activated the transcription ofisochorismate synthase 1(ICS1),respiratory burst oxidase homolog F(RbohF) and a few SAG genes. Consistently, the expression of these genes was reduced inwrky42mutants but was markedly increased in transgenic Arabidopsis overexpressingWRKY42. Bothin vitroelectrophoretic mobility shift assays (EMSAs) andin vivochromatin immunoprecipitation and dual luciferase assays demonstrated that WRKY42 directly bound to the promoters ofICS1andRbohF, as well as a fewSAGs, to activate their expression. Genetic analysis further showed that mutations ofICS1andRbohFsuppressed the early senescence phenotype evoked byWRKY42overexpression. Thus, we have identified WRKY42 as a novel transcription factor positively regulating leaf senescence by directly activating the transcription ofICS1,RbohFandSAGs, without any seed yield penalty.