淀粉磷酸化酶在木薯淀粉合成多酶复合体中的功能研究

Starch yield and quality are paramount agronomic traits of cassava, affecting its farming and industrial applications. On the basis of functional study of key enzyme genes in starch biosynthesis, regulation the expression level of those genes is the most effective means for starch quality improvements. Starch phosphorylase SP may function in starch biosynthesis associating with the activities of other key enzymes, resulted in altered starch structure and quality. However little is known about the specific function of SP. The project intends to carry out research on the function and mechanism of action for SP in cassava starch biosynthesis at different development stages of storage root. Through efficient genetic transformation platform, transgenic cassava plants are obtained with over-expression and down-regulated expression level of SP gene specifically. Research are focused on gene expression pattern and the enzyme activity regulation of SP, and combined with studies of starch-related phynotypes in transgenic cassava, the function of SP in storage starch biosynthesis will be uncovered. Research is also carried on transgenic cassava with down-regulated expression level of SBE gene to study the interaction of SP and other key enzymes. Through studying the interaction between SP and SBE among protein complexes of key enzymes, integrated the results of structural characteristics of high amylose starch and various carbohydrates, the contribution of SP to high amylose starch granules morphogenesis and starch accumulation will be revealed. Meanwhile, we obtain a group of new varieties with improvement of starch yield and quality. The project will deepen our understanding of starch biosynthesis in cassava storage root and its regulatory mechanism, thus provide theoretical basis and technology for cassava starch yield and quality improvement research, and accordingly promote cassava germplasm innovation.

淀粉产量和品质是木薯首要的农艺性状，影响种植业和产业应用。解析淀粉合成关键酶的生物学功能并进行表达调控是改良淀粉的最有效手段。淀粉磷酸化酶(starch phosphorylase, SP)参与淀粉生物合成过程并影响其它关键酶的活性，进而影响淀粉结构与品质的机制还知之甚少。本项目拟对木薯储藏根发育过程中SP参与淀粉合成的生物学功能开展研究。利用SP过表达或RNAi的转基因木薯，研究储藏根发育过程中SP的基因表达模式、酶活及调控方式对淀粉合成代谢的影响。同时结合淀粉分支酶(SBE)干扰下调的高直链淀粉转基因木薯，研究SP与SBE等关键酶的互作对葡聚糖产物结构组分的影响，进而解析SP对高直链木薯淀粉粒的形态结构和淀粉富集的作用。同时获得一批淀粉产量和品质改良的新种质新材料。该课题成果将深化我们对木薯储藏根淀粉生物合成及调控机理的了解，并为木薯淀粉产量和品质改良提供依据和技术，推动木薯种质创新。

本项目针对木薯储藏根发育过程中SP酶蛋白的功能以及储藏根淀粉合成关键酶之间的相互作用开展研究。揭示了SP酶的功能主要是在淀粉起始合成阶段通过影响短葡萄糖链（DP<25）的聚合分解从而调控储藏根发育过程中淀粉合成代谢。同时发现了木薯淀粉合成关键酶间相互作用的特点，是以淀粉合成酶SS、淀粉分支酶SBE、淀粉去分支酶ISA为主要成分形成了蛋白复合体，SP则可能参与复合体活性的磷酸化与去磷酸化调控过程。这些研究进一步完善了储藏根淀粉合成的机制模型，深化了对薯类淀粉生物合成的认识，从而在遗传改良木薯淀粉品质工作中能够更好的调控关键酶基因的表达，加快新品种的培育进程。本项目还培育出直链淀粉含量显著升高的iSBE转基因遗传株系，其具有新型物化特性与多元化的的优良淀粉品质，可供下游产品研发，将深入挖掘木薯淀粉应用潜力，拓展产业领域。