A NAC transcription factor BrNAC087 is involved in gibberellin-delayed leaf senescence in Chinese flowering cabbage

Phytohormone gibberellins (GAs) regulate leaf senescence. A global view of the regulatory pathways associated with GA-mediated inhibition of leaf senescence, especially in economically important leafy vegetables such as Chinese flowering cabbage, remains unclear. In this study, exogenous supply of gibberellin (GA3) delayed postharvest Chinese flowering cabbage leaf senescence. By comparative transcriptome analysis of leaf tissue, a total of 4682, 5059, and 2362 differentially expressed genes (DEGs) were identified between the comparison of 0d (cabbages at the harvest day) and CK3d (control cabbages at day 3 post-harvest), 0d and GA3d (GA3-treated cabbages at day 3 post-harvest), and CK3d and GA3d, respectively. Further analysis of identified DEGs involved in chlorophyll and GA degradation during leaf senescence, and the activity of chlorophyll catabolic genes (CCGs) BrPPH and BrRCCR, and bioactive GA degradation gene BrGA2ox1, was greatly reversed with GA3 application during leaf senescence. More importantly, a NAC transcription factor (TF), BrNAC087, was found to be associated with leaf senescence. BrNAC087 is a nuclear localized gene with transcriptional activity, highly expressed during senescence but downregulated by GA3. Significantly, BrNAC087 positively regulated BrPPH, BrRCCR and BrGA2ox1 expression by binding to NAC-binding sequences in their promoters in vitro and in vivo. These findings collectively provide evidence for a new molecular regulatory pathway explaining, at least in part, a mechanistic basis for gibberellin-mediated leaf senescence inhibition in postharvest Chinese flowering cabbage.