拟南芥幼年向成年转变的分子机制研究

The juvenile-to-adult transition (i.e. vegetative development) in plants is a paramountly important process partially in that it determines reproductive competence. It directly regulates plant resistance to biotic and abiotic stress, plant secondary compounds synthesis plant cell wall compenents, and plant architecture, etc. The transition of adult-to-reproductive phase (also known as flowering) is a well-studied process because of its obvious phenotypes associated with this transition. While, the mechsnism of the juvenile-to-adult transition remains unclear mainly due to the fact that the phenotypes associated with this developmental process are relatively subtle, and the much longer time it takes to complete this process. Recent research shows that miR156 is the master regulator of vegetative development in plants by regulating and coordinating different SPL (squamoso promoter binding-like proteins) genes. However, how miR156 itself is regulated by upstream external factors, what is the identity of the SPL targets remain elusive. We are very much interested in identifying these factors controlling miR156 expression and the targets of SPL proteins, as well as understanding their roles in vegetative development in Arabidopsis by using forward and reverse genetics, molecular biology and genomic approaches. The results we get from this project will provide some deeper clues to further our understanding of the molecular mechanisms of the juvenile-to-adult transition in plants.

植物幼年向成年转变（植物营养生长过程）是开花的基础。它直接调节植物抗病虫性、抗逆性，调控植物次生代谢产物合成及植物细胞壁组分，调控植物株型等，是一个十分重要的发育过程。前人已对植物从成年向生殖生长阶段转变（即开花）的分子机理进行了深入研究。不过，由于存在表型弱、转变周期长等特点，植物幼年向成年转变过程的研究十分滞后。最近研究表明,miR156是调控植物幼年向成年转变的主要调控因子。miR156通过调控并协调不同SPL（Squamosa promoter binding-like protein）基因的表达来调控该发育进程。然而，miR156是如何受到上游其它因子的调控，不同SPL基因的下游靶基因是什么，这些因子在植物营养生长中的功能是什么还不清楚。本项目将以拟南芥为研究对象，采用正反向遗传学、分子生物学及基因组学的方法研究上述问题，为深入了解植物从幼年向成年转变的分子机理提供基础。

miR156-SPLs是调控植物幼年向成年阶段转变保守的基因途径，但miR156如何受上游因子调控的研究积累较少。本项目执行期间，建立一套筛选miR156表达调控相关突变体的GFP筛选体系，通过EMS诱变、荧光及表型筛选，共获得突变体83份，其中幼年向成年阶段转变提前突变体（pre）31份，幼年向成年阶段转变延迟突变体（del）52份，这些突变体的获得为miR156表达调控研究提供了基础。图位克隆及二代测序共鉴定了10份突变体的候选基因。相关编码基因的功能涉及表观遗传学、miRNA加工合成和功能行使、叶绿体发育、mRNA转录起始等等。对其中pre1和del3突变体研究结果发现BRM所调控的核小体占位和SWN所调控的组蛋白H3K27me3修饰对MIR156A表达具有重要的调控作用，且上述两种表观遗传调控相互拮抗，共同调控拟南芥幼年向成年阶段转变发育过程。本项目执行期间还通过ChIP-Seq分析了SPL3和SPL9的结合位点，为研究SPLs下游调控网络提供了参考。

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