Abstract 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 decreasing 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.

中文翻译：

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BrNAC041在大白菜叶片衰老过程中ABA-GA拮抗作用的参与

摘要 众所周知，植物激素脱落酸 (ABA) 和赤霉素 (GAs) 在介导植物发育过程中具有拮抗作用。然而，在经济上重要的叶菜类蔬菜叶片衰老中，这种拮抗作用的潜在分子机制尚不清楚。在这项研究中，我们报道了一种大白菜 NAC 转录因子 BrNAC041，介导了 ABA 诱导的叶片衰老中 ABA 拮抗的 GA 积累。外源ABA处理加速大白菜叶片衰老，降低最大量子产量（Fv/Fm）和总叶绿素含量，并上调衰老相关基因的表达。值得注意的是，ABA处理增强了内源性ABA积累并降低了衰老叶片中的GA3水平。一贯地，在应用 ABA 后观察到一个 ABA 分解代谢基因 BrCYP707A3 和两个 GA 生物合成基因 BrKAO2 和 BrGA20ox2 的下调。此外，NAC 转录因子 BrNAC041（拟南芥 ANAC041 的同源物）被分离和表征。BrNAC041 被衰老-/ABA-上调并定位于细胞核中，作为转录抑制因子。进一步的体外和体内实验表明，BrNAC041 通过 NAC 结合序列 (NACBS) 靶向其启动子来抑制 BrCYP707A3、BrKAO2 和 BrGA20ox2 转录。总的来说，我们的研究结果揭示了 BrNAC041 作为一种新型调节剂，通过对 ABA 分解代谢和 GA 生物合成基因的转录抑制，参与了大白菜叶片衰老中 ABA 对 GA 的拮抗作用。