NAC转录因子参与植物激素GA和ABA交互调控的菜心叶片衰老的机制解析

Chinese flowering cabbage is one of the important leaf vegetables, however, its leaves are easy to senesce and become yellow after harvest, resulting in seriously economical loss. Thus, it is a noteworthy scientific topic to explore the regulatory mechanisms of leaf senescence of Chinese flowering cabbage . Diverse phytohormones regulate plant biological process synergistically or antagonistically through combination of complicated networks, and transcription factors play an important role in the crosstalks of phytohormones. Gibberellins (GA) and abscisic acid (ABA) is one pair of phytohormones which regulate leaf senescence antagonistically, while it is remained largely unknown how does this antagonistic effect occur between GA and ABA, and whether NAC transcription factors are involved in this antagonistic effect. In the present project, based on the selection of senescence-related NAC transcription factors in Chinese flowering cabbage, their responses to GA and ABA will be further investigated. Moreover, the direct targets, interaction proteins and biological functions of senescence-related NAC transcription factors will be confirmed though DNA-protein, protein-protein and transgenetic approaches, and subsequently, the molecular mechanism of NAC transcription factors involved in the crosstalk of GA- and ABA-mediated leaf senescence in Chinese flowering cabbage will be comprehensively explored. The results obtained by this project will not only deepen the understanding of plant leaf senescence, but also provide new theoretical foundation for improving postharvest preservation technology of Chinese flowering cabbage in practice.

菜心是一种重要的叶菜类蔬菜，但其采后叶片极易衰老黄化，导致严重的经济损失，因此研究菜心叶片衰老的调控机制是一个值得关注的科学问题。不同植物激素通过形成交互（crosstalk）的网络，协同或拮抗地调控植物生物学过程，而转录因子在其中发挥重要作用。赤霉素（GA）与脱落酸（ABA）在植物叶片衰老过程中表现出拮抗的生物学效应，但是，它们是如何实现拮抗效应以及NAC转录因子是否参与调控它们之间的交互？目前还知之甚少。本项目在筛选获得菜心叶片衰老相关NAC转录因子的基础上，进一步分析NAC转录因子对GA和ABA的响应，并通过DNA-蛋白质和蛋白质互作，以及转基因等手段，明确NAC转录因子的靶基因、互作蛋白以及生物学功能，进而对NAC转录因子参与GA与ABA交互调控的菜心叶片衰老的分子机制进行全面的解析。研究结果将加深对植物叶片衰老机理的认识，并为生产上改进菜心采后保鲜技术措施提供新的理论依据。

植物特有的一类转录因子NAC是主要的衰老调控因子之一。我们前期研究发现外源GA和ABA处理可以分别延缓和促进采后菜心叶片衰老；但菜心叶片衰老过程中，ABA和GA是否有交互，以及NAC转录因子是否参与了ABA-GA的交互，尚未见报道。..本项目中，证实了叶片衰老过程中ABA和GA有交互：外源ABA处理后明显增加了叶片内源ABA的积累，降低了GA含量，这与促进了ABA合成及GA降解基因，而抑制了ABA降解与GA合成基因的表达水平密切相关。..从差异表达的NAC中筛选获得了4个受ABA显著诱导的BrNAC041、BrNAC055、BrNAC087和BrNAC092，筛选获得了它们的互作蛋白BrWRKY6和BrABFs等，并对它们调控ABA-GA介导的菜心叶片衰老机制进行了系统分析。证实了BrWRKY6受到GA的抑制，并且分别激活和抑制叶绿素降解和GA合成基因的转录；BrABFs直接激活ABA合成和叶绿素降解基因的转录，而褪黑素抑制了ABF对这些基因的激活效应；BrNAC055直接激活叶绿素降解和活性氧合成基因的转录；BrNAC041直接抑制GA合成和ABA降解相关基因的表达；BrNAC087和BrNAC092均能直接激活衰老相关、叶绿素降解、ABA合成及GA降解基因的转录。上述研究结果建立了NAC/WRKY/ABF-ABA/GA之间的直接联系，为植物叶片衰老转录调控及其网络提供了新的观点，可为生产上改进菜心采后品质维持的贮运保鲜技术措施提供重要理论依据。..在本项目的资助下，已经在Journal of Pineal Research、Horticulture Research、Journal of Agricultural and Food Chemistry和Postharvest Biology and Technology等刊物上发表了9篇论文，培养了2名博士研究生。