赤霉素促进棉花纤维糖转运和次生壁合成的分子机理研究

Cellulose deposited in secondary cell wall, accounting for over 90% of cotton fiber weight, is the most important determinant of cotton productivity and quality. Our previous researches indicated that GA overproduction promoted secondary cell wall synthesis in cotton fiber, and down-regulation of GA signaling by expressing DELLA protein significantly decreased the expression of genes related to sugar transport and catabolism, and inhabited thickening of secondary cell wall. Further studies demonstrated that DELLA protein might control the expression of genes related to sugar transport and catabolism by interacting with MADS-box transcription factors, implying that GA might control the secondary cell wall synthesis through the pathway of DELLA-MADS-sugar transport and catabolism. In addition to clarify the relationships among GA, DELLA proteins, MADS-box transcription factors and genes related to sugar transport and catabolism, this project will adopt transgenic method to evaluate the influence of sugar transporters and MADS-box transcription factors on sugar transpot and utilizationm, and cellulose synthesis during the stage of secondary cell wall synthesis, and the final productivity and quality of cotton fiber. This may elucidate the molecular base for GA to regulate carbon partitiooning and secondary cell wall biosynthesis in cotton fiber, and pave the way to improve cotton yield and quality, and even source-sink relationships in other crops biotechnologically.

棉花纤维次生壁合成期积累的纤维素占成熟纤维干重的90%以上，是棉花产量和品质最重要的决定因素。前期研究表明，上调赤霉素（GA）水平促进棉花纤维次生壁和纤维素合成，而表达DELLA蛋白下调GA信号显著降低糖转运和代谢相关基因的表达，并抑制纤维次生壁增厚，同时DELLA蛋白与MADS-box转录因子相互作用调控棉花糖转运和代谢相关基因的表达。这些结果暗示GA通过DELLA-MADS-糖转运和利用的信号途径调控纤维次生壁合成。本项目拟首先深入分析GA、DELLA蛋白、MADS-box转录因子及糖转运和代谢相关基因表达的关系，在此基础上，利用转基因手段评价糖转运蛋白和MADS-box转录因子对棉花次生壁合成期纤维糖转运与利用、纤维素合成和纤维产量品质的影响，阐明GA调控棉花纤维糖转运利用和次生壁合成的分子机制，为纤维产量和品质的基因工程改良，以及植物的源-库关系调节奠定理论基础。

赤霉素（Gibberellins, GAs）是重要的植物激素，在植物中GA具有保守的信号传导组分和途径。长期以来，GA被认为是调节库源关系的重要因素。本项目试图利用棉花纤维为材料揭示GA信号途径与植物糖转运和碳分配之间的调控关系。我们的研究显示，在纤维次生壁合成期特异上调DELLA蛋白抑制次生壁沉积，而下调纤维优势表达的SWEET基因的表达水平促进次生壁沉积，表明GA-DELLA信号和糖转运均参与靶向纤维的碳分配和次生壁合成的调控。同时，我们通过鉴定DELLA互作蛋白揭示了以DELLA蛋白为中心的包括多种激素信号和多种转录因子的复杂调控网络，为进一步阐明棉花纤维发育和碳分配的调控奠定了基础。