Involvement of BrNAC041 in ABA-GA antagonism in the leaf senescence of Chinese flowering cabbage

Phytohormone abscisic acid (ABA) and gibberellins (GAs) are well-known to be antagonistic in mediating plant development processes. However, the underlying molecular mechanism of this antagonism in leaf senescence of economically important leafy vegetables is largely unclear. In this study, we report that a Chinese flowering cabbage NAC transcription factor BrNAC041, mediated the ABA-antagonized GA accumulation in ABA-induced leaf senescence. Exogenous ABA treatment accelerated Chinese flowering cabbage leaf senescence, with de-creasing maximum quantum yield (Fv/Fm) and total chlorophyll content, as well as up-regulating the expressions of senescence-associated genes. Notably, ABA treatment enhanced endogenous ABA accumulation and reduced GA3 level in senescing leaves. Consistently, down-regulation of one ABA catabolism gene BrCYP707A3 and two GA biosynthesis genes BrKAO2 and BrGA20ox2 was observed following ABA application. Furthermore, a NAC transcription factor, BrNAC041, a homolog of Arabidopsis ANAC041, was isolated and characterized. BrNAC041 was senescence-/ABA-up regulated and localized in the nucleus acting as a transcriptional repressor. Further in vitro and in vivo experiments demonstrated that BrNAC041 repressed BrCYP707A3, BrKAO2 and BrGA20ox2 transcription by targeting their promoters via the NAC-binding sequence (NACBS). Collectively, our findings reveal BrNAC041 as a novel regulator involved in the antagonism of ABA on GA in the leaf senescence of Chinese flowering cabbage, through the transcriptional repression of ABA catabolic and GA biosynthetic genes.