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 that WRKY42 was highly induced during leaf senescence. Loss-of-function wrky42 mutants showed delayed leaf senescence while overexpression of WRKY42 accelerated senescence. Transcriptome analysis revealed 2,721 differentially expressed genes between wild type and WRKY42-overexpressing plants, including those whose encoded proteins are involved in salicylic acid (SA) and reactive oxygen species (ROS) synthesis as well as several senescence-associated genes (SAGs). Moreover, WRKY42 activated the transcription of Isochorismate Synthase 1 (ICS1), Respiratory burst oxidase homolog F (RbohF) and a few SAG genes. Consistently, expression of these genes were reduced in wrky42 mutants but markedly increased in transgenic Arabidopsis overexpressing WRKY42. Both in vitro electrophoretic mobility shift assays (EMSA) and in vivo chromatin immunoprecipitation and dual-luciferase assays demonstrated that WRKY42 directly bound to the promoters of ICS1, RbohF as well as a few SAGs to activate their expression. Genetic analysis further showed that mutations of ICS1 and RbohF suppressed the early senescence phenotype evoked by WRKY42 overexpression. Thus, we have identified WRKY42 as a novel transcription factor positively regulating leaf senescence by directly activating the transcription of ICS1, RbohF and SAGs, without seed yield penalty.