Characterization of a Transcriptional Regulator, BrWRKY6, Associated with Gibberellin-Suppressed Leaf Senescence of Chinese Flowering Cabbage.

Phytohormone gibberellin (GA) and plant-specific WRKY transcription factors (TFs) are reported to play important roles in leaf senescence. The association of WRKY TFs with GA-mediated leaf senescence of economically important leafy vegetables like Chinese flowering cabbage, however, remains largely unknown. In this study, we showed that exogenous application of GA3 suppressed Chinese flowering cabbage leaf senescence, with GA3-treated cabbages maintaining a higher level of maximum quantum yield (Fv/Fm) and total chlorophyll content. GA3 treatment also led to lower electrolyte leakage and expression level of a series of senescence-associated genes (SAGs) including BrSAG12 and BrSAG19, and chlorophyll catabolic genes (CCGs) BrPPH1, BrNYC1, and BrSGRs. In addition, higher transcription levels of GA biosynthetic genes BrKAO2 and BrGA20ox2 were found after GA3 treatment. More importantly, a GA-repressible, nuclear-localized WRKY TF, BrWRKY6, a homologue of the Arabidopsis AtWRKY6, was identified and characterized. BrWRKY6 was GA-repressible and localized in the nucleus. Further experiments revealed that BrWRKY6 repressed the expression of BrKAO2 and BrGA20ox2, while it activated BrSAG12, BrNYC1, and BrSGR1, through binding to their promoters via the W-box cis-element. Together, the novel GA-WRKY link reported in our study provides new insight into the transcriptional regulation of GA-suppressed leaf senescence in Chinese flowering cabbage.