谷氨酰胺合成酶调控拟南芥幼年向成年阶段转变的分子机制研究

The juvenile-to-adult transition in plants is a vital developmental process in that it regulates plant response to abiotic and biotic stress, establishment of plant architecture, plant secondary metabolism, and other numerous physiological and biochemical pathways. miR156 is the master regulator of this developmental process, and its expression is regulated by both endogenous and exogenous factors. However, how miR156 is regulated by exogenous factors and the function of these exogenous factors in the juvenile-to-adult transition remain elusive. In a forward genetic screen, we identified that loss-of-function mutation in the Arabidopsis gene glutamine synthetase 2 (GS2) exhibited a delayed vegetative phase change phenotype. In this study, we will study the molecular mechanism of GS2-mediated regulation of miR156 expression and the function of interplay between N and C assimilation and metabolism in the regulation of juvenile-to-adult transition in Arabidopsis using a combination of forward and reverse genetics, molecular biology, physiology and biochemistry and genomics. Our research here will provide a basis to further understand the mechanism underlying the regulation of miR156 and the juvenile-to-adult transition in plants.

植物幼年向成年阶段转变调控植物对生物与非生物胁迫响应、植物株型建成及植物次级代谢产物合成等多种生理、生化途径，是一个非常重要的发育过程。miR156是调控植物幼年向成年阶段转变的主控因子，其表达受内外因子调控。然而环境因子是如何调控miR156的表达以及这些因子如何在植物幼年向成年阶段转变中发挥功能还不是很清楚。本项目将以筛选到的具有幼年向成年阶段转变延迟表型的拟南芥谷氨酰胺合成酶2缺失突变体 (glutamine synthetase 2, GS2)为研究对象，采用正反向遗传学、分子生物学、生理生化及基因组学的方法来研究GS2介导的N同化与代谢途径调控miR156表达的分子机制以及N代谢途径如何与C代谢途径互作协调来调控拟南芥幼年向成年阶段转变。该研究结果将为今后深入了解植物miR156表达调控以及幼年向成年转变的分子机理提供基础。

植物幼年向成年阶段转变调控植物对生物与非生物胁迫响应、植物株型建成及植物次级代谢产物合成等多种生理、生化途径,是一个非常重要的发育过程。miR156是调控植物幼年向成年阶段转变的主控因子，其表达受内外因子调控。然而环境因子是如何调控miR156的表达以及这些因子如何在植物幼年向成年阶段转变中发挥功能还不是很清楚。本项目以筛选到的具有幼年向成年阶段转变延迟表型的拟南芥谷氨酰胺合成酶2缺失突变体(glutamine synthetase 2,GS2)为研究对象，采用正反向遗传学、分子生物学、生理生化及基因组学的方法研究了GS2调控miR156表达的分子机制。结果表明，gs2中miR156成熟体含量及其主效前体MIR156A和MIR156C的表达水平皆显著上调，miR156靶基因SPL9下调,SPL9的直接下游靶基因MIR172B及成熟体miR172均显著下调。遗传分析证实miR156位于GS2下游，GS2通过调控miR156的表达进而调控拟南芥营养生长阶段转变。对gs2转录组分析发现，GA合成途径基因GA20OX1表达显著下降，而GA降解代谢途径基因Ga2OX4表达显著上升。相应地，GA1,GA3,GA4三种活性GA在gs2中均显著下降。GA3喷施gs2可部分回复其幼年向成年阶段转变延迟的表型。利用H3K4me3及H3K27me3抗体ChIP分析发现,在gs2中H3K4me3在MIR156A和MIR156C前体启动子上有显著富集，而H3K27me3修饰却显著降低。说明GS2通过调控MIR156A和MIR156C前体启动子位点上组蛋白的修饰来调控miR156前体的转录。该研究结果为今后深入了解植物miR156表达调控以及幼年向成年转变的分子机理提供了理论基础。