Regulation of reactive oxygen species production by LrWRKY53 transcription factor promotes leaf senescence and Botrytis cinerea susceptibility in lily.
WRKY transcription factors (TFs) play regulatory roles in leaf senescence and resistance to biotic stress. Elucidation of the underlying regulatory mechanisms is crucial for improving crop performance and resistance. However, functional characterization of WRKY TFs in Lilium species is limited. Here, three Botrytis cinerea-responsive genes, LrWRKY33b, LrWRKY41b, and LrWRKY53, were cloned from L. regale Wilson and transiently expressed in tobacco to investigate the specific role of LrWRKY53 in leaf yellowing. LrWRKY53 is a 308-amino-acid cluster III protein encoded by a 927-bp open reading frame. Tissue-specific analysis showed that LrWRKY53 was significantly upregulated in senescent leaves and was responsive to salicylic acid (SA) and jasmonic acid (JA) signaling. LrWRKY53 was localized to the nucleus and demonstrated transcriptional activity in yeast cells. Transient overexpression of LrWRKY53 in lily plants induced leaf yellowing and increased susceptibility to Botrytis cinerea infection, which was suppressed on downregulation of LrWRKY53. LrWRKY53 overexpression led to significantly increased levels of hydrogen peroxide and the oxygen anion (O2-). Moreover, overexpression of LrWRKY53 in Arabidopsis promoted leaf senescence and enhanced B. cinerea susceptibility, which coincided with increased production of reactive oxygen species (ROS) and upregulation of the associated respiratory burst oxidase homolog (AtRboh)A and AtRbohD genes. Furthermore, yeast one-hybrid and transactivation assays indicated that LrWRKY53 activated the promoter of LrRBOH1 isolated from L. regale. Collectively, this is the first report of a WRKY regulator mediating leaf senescence and B. cinerea susceptibility in lily through its effects on ROS homeostasis.