新转录因子DIT1调控拟南芥叶片发育

Leaves are the major organs for photosynthesis. Many factors including endogenous signals such as various hormones and environmental cues such as fertilizer and water all affect leaf final sizes and shapes. The regulation of leaf development is rather complicated. Up to now, the mechanisms controlling leaf growth and development are still elusive. Here, we found a novel transcription factor DIT1 (DELLA Interacting Transcription factor 1) which interact with the known DELLA transcription repressor RGA though screening our Gal4-AD transcription factor library for DELLA interactors. BiFC confirmed the interaction between DIT1 and RGA. Overexpression of DIT1 led to severe leaf defects including small sizes and shape abnormalities, suggesting that DIT1 plays key roles in leaf development. This study will demonstrate the mechanisms by which DIT1 regulate leaf development by genetic and molecular approaches. The detailed phenotypes of leaves caused by overexpression or disruption of DIT1 will be investigated. The expression pattern of DIT1 in leaves will be examined. We will confirm the interaction between DIT1 and RGA and find the interaction domains in these two proteins. The downstream genes directly regulated by DIT1 will be found out to illustrate the molecular mechanisms by which DIT1 modulate leaf development.

植物叶片是光合作用的主要器官。很多因素包括内源信号和外界环境都影响叶片的最终形状和大小。植物叶片的发育调控机制到目前仍不十分清楚。通过DELLA蛋白RGA作为诱饵筛选本实验室的拟南芥转录因子库，从中筛选到一个新的RGA相互作用的蛋白DIT1(DELLA Interacting Transcription factor 1). 通过BiFC进一步证明RGA和DIT1确实在体内相互作用。DIT1定位在核中。过量表达DIT1导致叶片严重变形且变小。初步研究表明该基因在叶中表达。说明DIT1在植物叶片发育中起到关键的调控作用。本研究将调查DIT1过量表达和功能失活后造成叶片缺陷的详细表型，研究该基因在叶片中的表达模式，进一步验证DIT1与RGA相互作用，包括寻找它们相互作用的蛋白区域，同时将寻找转录因子DIT1的直接调控的下游基因，最终阐明DIT1调控叶片发育的分子机制。

植物分枝在植物通过形态可塑型适宜环境以及农业生产中最佳株型的育种实践中起到重要作用。植物分枝形成需要先形成叶腋分生组织进而发育成腋芽，而腋芽活性决定其是否能进一步形成分枝。包括“腋芽分生组织调控因子”（REGULATOR OF AXILLARY MERISTEMS 1，RAX1），RAX2和RAX3基因在内的多个编码转录因子的基因在调控叶腋分生组织和腋芽的形成中起关键作用，但植物分枝的调控网络仍很不清楚。本研究发现了一个新的因子EXB1通过影响腋芽的形成和腋芽活性进而控制植物分枝的形成。本研究通过筛选获得一个T-DNA插入激活突变体exb1-D，分枝表型观察和统计分析表明过量表达EXB1促进腋芽的形成并提高了腋芽活性。通过分子生物学研究和遗传重现实验确定了EXB1编码一个功能未知的WRKY类转录调控因子WRKY71。EXB1在腋芽中优势表达，其所编码的蛋白定位在核中并具有转录激活活性。通过显性失活的方法确定了EXB1功能缺失可抑制植物分枝形成，进一步说明了EXB1在植物分枝过程中的重要作用。通过诱导表达实验和转录组测序（RNA-seq）分析了EXB1调控的下游基因，并在调控的下游基因中找到了RAX1，RAX2和RAX3基因受EXB1直接调控，同时还发现EXB1也通过影响植物体内生长素的稳态，揭示了EXB1调控植物分枝的分子机制。这些结果表明EXB1是调控植物分枝的关键因子，通过调控RAX基因和生长素的稳态来起作用。