GhTUB17基因在纤维发育中的功能和调控机制

Microtubule plays an important role in the growth and development of cotton fibers. However, the regulatory mechanism of microtubule dynamics in fiber development and the molecular basis of fiber development regulated by microtubule are largely unknown. We have found that the expression level of GhTUB17 gene decreased significantly in the fiber of li-1 mutant, a monogenic dominant mutant characterized by abnormal lint fiber development, bears very short lint fibers, when compared with the expression levels of tubulin genes in the fibers of wildtype. The GhTUB17 gene expressed preferentially in fibers and the peak was at the stage of fast fiber elongation. Furthermore, two DNA regions were deficit in the promoter of GhTUB17 gene from li-1 mutant when compared with the promoter sequence from wildtype. There are a few BRs response motifs in the deficit regions. Based on these results, we will illuminate the effects of over-expressing or suppressing GhTUB17 on the dynamics of microtubules and the development of fibers in transgenic cotton plants in this study. On the other hand, the expression pattern of the promoter of GhTUB17 gene from wildtype or li-1 mutant will be determined by transgenic cotton plants and the response to various phytohormones for these promoters will be detected using transgenic plants. Furthermore, the binding activities of the promoters to the GhBES1/GhBZR1 protein, a transcript factor involved in BRs signaling, will be analyzed. In addition to, the expression diversity of important genes involved in key pathway for fiber development will be detected. By these studies, the function and regulatory mechanism of GhTUB17 in the growth and development of fibers will be revealed. The molecular basis on the retard fiber cell of li-1 mutant and the action of GhTUB17 on the microtubule dynamics will be illuminated.

微管在纤维发育中有重要作用，但微管调控纤维发育的分子机理还不清楚。申请人对比了超短纤维突变体和野生型纤维伸长期的基因表达差异，发现GhTUB17在突变体纤维伸长期的表达远低于野生型，而且在纤维中优势表达并在快速伸长期达到高峰，表明该基因与纤维伸长有密切关系。进一步研究发现，突变体中该基因启动子有两段缺失并由此丧失较多BRs响应元件，暗示该基因受BRs调控且在纤维伸长中发挥重要作用。但具体作用尚不明确。为了阐明该基因在纤维发育中的功能和调控机制，本研究拟通过调节GhTUB17基因在纤维中的表达，观测其对纤维发育的影响和对微管微丝排列的调控；同时比较来源于野生型和突变体的GhTUB17启动子在纤维中的表达特性和对激素的响应，进而分析性状变异的转基因纤维中重要代谢途径及相关基因表达变化，分析基因调控网络。为解析纤维发育机制提供新的证据，为纤维品质改良基因工程提供理论依据、目标基因和调控序列。

棉花纤维是胚珠外珠被发育而成的单细胞，微管在纤维细胞生长发育过程中具有重要作用，但微管调控纤维发育的分子机制还不清楚。本项目研究GhTUB17基因在纤维细胞生长发育中的功能和相应的作用机理，分析GhTUB17基因5'-上游调控序列的表达特征、核心调控序列和影响因素，分析GhTUB17基因启动子与BRs信号传导转录因子BZR1的结合特性，检测了GhTUB17对纤维发育中微管微丝动态变化和排列特性的影响等方面。结果表明在转基因棉花纤维细胞中上调和下调GhTUB17基因的表达能明显促进和抑制纤维细胞的伸长，说明该基因在纤维伸长过程中具有重要作用，其表达水平与纤维长度具有对应关系。上调GhTUB17能够促进纤维发育早期微管横向排列并稳定纤维伸长后期的微丝结构，可能是促进纤维细胞伸长的主要原因。GhTUB17基因1400bp的启动子序列是调控GhTUB17基因表达的核心序列，在1400-1900bp间存在转录增强序列。同时900bp启动子序列具有纤维细胞表达特异性，是一个纤维伸长期特异表达的调控序列。GhTUB17基因的表达受到BZR1转录因子的调控。这些结果阐明了GhTUB17基因在纤维细胞生长发育中的功能和作用机制，以及调控该基因表达的分子机制，为利用基因工程改良纤维品质提供了有效的目的基因和纤维细胞伸长期特异表达的调控序列，同时明确了油菜素类固醇激素-细胞骨架-纤维发育的网络关系，为解析棉花纤维的生长发育提供了新的证据。