GI介导干旱胁迫响应和干旱逃逸的分子机理

Drought will reduce crop yields, thus it is of great significance to improve the drought tolerance of the crops. The plants have evolved some strategies to adapt to drought stress,such as to accelerate flowering, a phenomenon called drought escape (DE). Flowering time is regulated by several pathways, however, the DE response has not yet been ascribed to which pathway. The previous study of our lab has revealed that the photoperiod pathway might be involved in the DE response. The loss-of-function mutant of GIGANTEA (GI), which is a key component of photoperiod pathway, exhibited abnormal DE response. The mature miR172e, downstream gene for GI, accumulated after drought stress. Therefore, GI may regulate DE response through miR172-FT pathway. Meanwhile, the gi mutant was sensitive to drought stress, which suggested that GI could plays roles both in drought defense and DE response. Our study aims to find the answers to the following questions, 1) How is FT regulated by GI and whether WRKY44 which was proved to interact with TOE1 in our previous study also acts in FT regulation; 2) In addition gi mutants exhibit an enhanced starch accumulation, so whether starch metabolism or carbon signaling function in flowering; 3) what genes does GI regulate in drought stress response. To establish the regulation network of DE response and drought defense based on the function of GI will provide theoretical foundation and genetic tools for increasing the crop yields and drought tolerance.

干旱严重影响农作物产量，提高其耐旱性意义重大。植物对于一定程度的干旱表现为提前开花，即干旱逃逸。植物开花时间由多条通路控制，但哪些通路参与调控干旱逃逸有待研究。本室研究发现光周期通路可能参与其调控，因为此通路中的重要调控子GIGANTEA(GI)的突变体无干旱逃逸能力。干旱下，GI下游成熟miR172E含量上升，GI可能通过miR172调控Flowering Locus T(FT)而控制开花。gi突变体对干旱敏感，因此GI具有维持干旱下植物生存和传播后代双重作用，这些结果为揭示干旱逃逸奠定基础。本课题拟阐明1）干旱下GI如何调控FT，前期发现与miR172下游基因TOE1互作的WRKY44是否参与此过程；2）gi突变体有糖积累的表型，糖代谢或糖信号转导是否参与干旱胁迫；3）GI调控哪些胁迫响应基因。以期建立以GI为中心的干旱逃逸和胁迫响应调控网络，为遗传改良作物性状提高产量奠定理论基础。

GI如何调控干旱下的提前开花，本研究通过染色质免疫沉淀实验（ChIP-PCR）发现GI可以结合WRKY44的启动子。将gi-2与WRKY44过表达株系杂交后，可以显著使gi-2突变体提前开花。然而，将ft-10与WRKY44过表达株系杂交后发现ft-10不能延迟WRKY44过表达早花的表型，暗示WRKY44调控开花时间并非通过FT途径。通过酵母单杂交实验发现WRKY44蛋白可以与花分生组织特异性基因 FUL的启动子相互作用。WRKY44作为GI的靶基因，既受GI的直接调控，同时又对FUL起转录调控，最终促进拟南芥提前开花。. G也I参与了CBF(C-repeat Binding Factor)通路的低温胁迫响应过程。结果表明GI位于CBF的上游，gi-2突变体中，CBFs及其下游基因的表达量上调；ChIP-PCR发现GI蛋白可以结合在CBF3的启动子上；酵母双杂交与烟草双分子荧光互补实验均证明GI与ICE1蛋白体内互作。并且GI与HOS1(HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 1)蛋白存在互作。以上结果表明GI可能通过HOS1来调控ICE1的蛋白水平，参与CBF介导的低温胁迫响应，相关的研究仍需要进行。