BrWRKY8: A Key Regulatory Factor Involved in Delaying Postharvest Leaf Senescence of Pakchoi (Brassica rapa subsp. chinensis) by 2,4-Epibrassinolide

Abstract

Brassinosteroids (BRs) are extensively distributed in plants and play crucial roles throughout all stages of plant growth. Nevertheless, the molecular mechanism through which BRs influence postharvest senescence in pakchoi remains elusive. Previous studies have demonstrated that application of 1.5 μM of the BRs analog 2,4-epibrassinolide (EBR) delayed the leaf senescence in harvested pakchoi. In this study, we constructed the EBR-delayed senescence transcriptome in pakchoi leaves and discovered that EBR modulates the expression of genes involved in the chlorophyll (Chl) metabolism pathway and the BRs pathway in pakchoi. Notably, we identified and characterized an EBR-suppressed, nucleus-localized WRKY transcription factor (TF) called BrWRKY8. BrWRKY8 is a highly expressed transcriptional activator in senescent leaves, targeting the promoters of the Chl degradation associated gene BrSGR2 and the BRs degradation associated gene BrCHI2, thereby promoting their expression. Overexpression of the BrWRKY8 gene accelerated the senescence process in Arabidopsis leaves, while EBR treatment mitigated the leaf senescence phenotype induced by BrWRKY8 overexpression. Conversely, silencing of BrWRKY8 through the virus-induced gene silencing (VIGS) extended the postharvest storage period of pakchoi. In conclusion, the newly discovered BRs-BrWRKY8 regulatory model in this study provides novel insights into BRs-mediated leaf senescence in pakchoi.