百脉根侧芽缺失突变体ljss1及相关基因的克隆和功能分析

Crop productivity highly depends on plant architecture and status, which is determined by the activity of axillary meristems formed in the postembryonic stage. The initiation of axillary meristem as well as its outgrowth are determined by the genetic constitution, developmental stage, and environmental conditions. The genetical mechanisms controling the iniation of axillary meristems are believed complicated, whereas our knowledge in this field remains limited. Axillary buds in the model legume Lotus japonicus are morphologically visible, and can continuelly develop into axillary shoots with little influence by apical dominance, which makes this tiny legume a good model to study axillary meristem initiaion. We previously obtained a Lotus japonicus mutant with no branches, which we termed ljss1 (single-stem 1). We propose to futher characterize this mutant in more details, and obtain the causal gene by map-based cloning. Further, we will study this ortholog of the LJSS1 gene in Arabidopsis by obtaining lost of function mutants. In addition to analysing phenotypic effects in Arabidopsis, We will also dissect the genetic interactions between the orthologous genes of LJSS1 in Aarabidopsis and other genes affecting axillary initiaiton. By analying how the LJSS1 gene regulates axillary meristem initiation in Lotus japonicas and in Arabidopsis, our study will provide new clues towards the understanding of how a stem cell niche can reestablish during postembryonic development.

农作物的产量很大程度的上取决于其植物形态和结构，而植物的形态和结构主要是由胚胎后发育中侧生分生组织的活力和数目决定。调控侧生分生组织起始过程的遗传机制是非常复杂的，但是迄今为止我们所得到的调控因子还很少。豆科模式植物百脉根的侧芽在形态学上易于观察，而且其生长不受顶端优势的影响，一旦侧芽产生都能直接发育为侧枝，非常易于表型鉴定。本项目拟利用百脉根作为研究侧芽发育的模式植物，通过对我们已有的侧芽缺失突变体ljss1进行表型分析，并通过图位克隆获得LJSS1基因从而进行功能分析。我们拟进一步对该基因在拟南芥中的同源基因进行突变体的表型分析和基因功能分析，从而解释该基因与已知侧芽相关基因的遗传学关系。通过在百脉根和拟南芥中全面解析LJSS1调控侧芽发育的分子机理，并比较百脉根和拟南芥侧芽发育在分子水平的异同，我们的工作将为植物侧生分生组织中心重建的调控机制提供新的线索。

植物地上部分的最终结构主要是由胚胎后发育阶段在叶腋处形成的侧生分生组织决定的。侧生分生组织的发育主要分为两个阶段：侧生分生组织的起始以及侧芽的外生。侧芽的外生主要受生长素、细胞素和独脚金内酯的调控，已经被系统的阐述。而侧生分生组织的起始虽然已经有一些报道，但是仍然知之甚少。本研究通过反向遗传学手段，筛选到一个侧芽起始相关基因AMD1（AXILLARY MERISTEM DEFECT1）基因。同等生长条件下，野生型侧芽起始率为84%，而突变体amd1的侧芽起始率只有26%。AMD1的两个同源基因的双突变体amd2 amd3具有很强的侧芽缺失表型，因此AMD家族在侧芽起始方面具有功能冗余性。.AMD1在比较年轻叶子的近轴面和叶腋处的细胞核中积累。当在突变体的叶腋处特异性表达AMD1时，突变体的侧芽缺失表型回复到了野生型水平，说明叶腋处AMD1是通过细胞自主性的方式调控侧芽起始。通过遗传学分析，AMD1可能与RAX1位于同一途径，且位于RAX1上游。细胞学研究发现，AMD1是通过影响STM叶腋处的信号稳定性来调控侧芽起始。转基因植物RPS5A::KNOX（STM） amd1增强了突变体侧芽缺失的表型，说明AMD1与STM之间存在之间直接相互作用。这些数据说明了AMD1通过调控叶腋处侧生分生组织稳定性来参与侧芽的起始过程。