水稻组蛋白甲基转移酶SDG724在种子休眠和萌发中调控机制

Seed dormancy and germination is the most intensively studied processes in plant development.It is closely related to agricultural production, such as precocious germination in many cereal crops termed as preharvest sprouting (PHS) or vivipary, which seriously affects the yield and grain quality of cereal crops. Many of these factors mediated by hormones,such as gibberellin (GA),ABA and major regulators controling seed maturation are all known to be involved in the process. Recently, chromatin modifications are also reported to be involved in the regulation of seed dormancy and germination in Arabidopsis. However, little is known about the underlying mechanism.Our previous research had cloned a histone methyltransferase gene SDG724 and demonstrated it had an important role in regulating flowering time in rice. Furthermore sdg724 also exhibited increased seed dormancy and germination defects and the expression of some major regulators controling seed maturation were changed; moreover the expression of SDG724 was induced by exogenous ABA. What could be the molecular mechanisms that SDG724 control the dormancy and germination in rice? This project based on a previous study, on the one hand, we want to understand how SDG724 and ABA control dormany and germination by SDG724/Osaba1 double mutant; on the other hand, we try to figure out the relationship between SDG724 and the major regulators controlling seed maturation, such as OsFUS3,OsLEC1 by microarray and chip-sequence, thus revealing the molecular mechanism for SDG724 in the control of seed dormany and germination. This project will provide theoretical basis for improving PHS in rice and other cereals.

种子休眠和萌发是重要的生物学基础问题，也与农业生产密切相关。有关种子休眠和萌发的生理生化机制已有深入研究：明确了植物激素ABA、GA及种子成熟过程中关键调控因子如FUS3，LEC1/LEC2等参与了这一过程。最近发现染色质修饰在种子休眠和萌发中起重要作用。我们前期克隆了水稻组蛋白甲基转移酶SDG724基因，阐述了其在开花途径中作用。进一步发现该突变体具有休眠性增强和萌发缺陷表型；其中一些种子成熟关键因子表达在萌发过程中发生了显著变化，并且SDG724表达受外源ABA诱导。本申请拟从遗传学上利用sdg724/ Osaba1等双突变体揭示SDG724与植物激素ABA的关系；生化和分子生物学上采用基因芯片、ChIP-Seq等手段来解析SDG724与种子成熟相关因子如OsFUS3，OsLEC1等的关系，从而揭示SDG724参与调控种子休眠和萌发的分子机制，最终为禾谷类粮食作物穗发芽的控制提供支持。

表观遗传学最近几年来突飞猛进，尤其是染色质修饰的研究取得了重要的进展，主要包括DNA甲基化酶和组蛋白修饰酶的研究，还有一些染色质调控因子也参与其中。如拟南芥的EBS蛋白能结合H3K4组蛋白标记，并且和组蛋白去乙酰化酶HAD6互作，从而抑制FT的表达来调控拟南芥的开花；同时EBS也调控了种子休眠，其突变体休眠性降低，其抑制休眠的AGL67表达也下调。我们早期克隆了一个组蛋白甲基化酶SDG724，阐述了其在水稻抽穗期调控方面的重要作用；进一步发现该突变体休眠性增强，种子萌发有一定缺陷。以此为切入点，试图通过正向遗传学（通过构建双突变来揭示其与相关突变体的遗传关系）和反向遗传学（构建一些种子发育关键基因转基因株系）来阐述其机制。. 本项目以SDG724为基础，筛选到两个恢复萌发的突变体phs8和phs9; 通过图位克隆结合重测序技术，我们克隆了这两个突变基因。PHS8编码一个糖合成基因，该突变体除了穗发芽，还表现出淀粉合成的缺陷；进一步功能分析发现，PHS8不受SDG724修饰，而参与了糖和ABA来控制休眠和萌发；PHS9是一个组蛋白去甲基化酶基因，他可能拮抗SDG724对组蛋白H3K36二甲基或者三甲基修饰激活基因的影响，而对基因起抑制作用；表达谱分析，初步确定水稻OsABI3是他们修饰的靶基因。他们通过调控OsABI3表达来调控水稻的休眠和萌发。