作物淀粉生物合成与转基因修饰研究进展

Advance in Starch Biosynthesis and Transgenic Modification in Crops

淀粉是高等植物中碳水化合物的主要贮藏形式 ,也是粮食作物产品的最主要成分。淀粉虽然都由直链淀粉和枝链淀粉组成 ,但在不同作物中两者的比例和枝链淀粉结构的存在很大差异。现已明确 ,直链淀粉是在颗粒结合淀粉合成酶 (granule boundstarchsynthase,GBSS)催化下合成的 ,而枝链淀粉是四种酶共同作用的结果 ,它们分别是腺嘌呤 -葡萄糖焦磷酸化酶 (ADP glucosepyrophosphorylase ,AGP) ,可溶性淀粉合成酶 (solublestarchsynthase ,SSS) ,淀粉分枝酶 (starchbranchingenzyme ,SBE)和脱分枝酶 (starchdebranchingenzyme ,DBE)。一方面 ,在不同作物中 ,这些酶本身存在多种形式 ,如在玉米胚乳中 ,AGP有大亚基和小亚基之分 ,SBE又可分BE1,BEIIa ,BEIIb 3种 ,SSS也可分为SSI和SSIII(或SSIIa)两种 ,而DBE也有异淀粉酶 (isoamylase)和限制性糊精酶 (pullu lanase)两种。另一方面 ,控制特定酶的基因 ,在不同作物甚至在同一种作物的不同品种中也可能存在不同的复等位基因 ,如籼稻和粳稻的GBSS分别由蜡质基因Wxa 和Wxb 控制 ,两者编码的GBSS活性差异显著。此外 ,环境条件也可通过影响基因的转录使酶的含量或催化性能发生变化。迄今 ,国内外已获得多种马铃薯和水稻的转基因材料 ,对淀粉合成进行修饰 。

Starch is the major storage carbohydrate in higher plants, and also the most important ingredient in food crops. Starch property varies greatly due to amylose to amylopectin ratio and amylopectin structure, which consequently influences its function and utility. In recent years, rapid progresses have been achieved towards the molecular biology of starch synthesis, nearly all related genes or gene fragments have been cloned. Starch synthesis starts with the formulation of Glucose-1-ADP catalyzed by ADP-glucose pyrophosphorylase, and more glucose are added by various starch synthases, such as soluble starch synthase (SSS), starch branching enzyme (SBE), granule-binding starch synthase (GBSS). It is then modified by debraching catalyzed by debranching enzyme (DBE), and elongated to some extent catalyzed by SSS and finally forms into starch granules. It has been know that the amylose syntheses are catalyzed by GBSS, while amylopectin by all in concerts. All these enzymes above have found being in multiform, for instance, in maize endosperm, AGPase consist of big and small subunits, SBE has isoforms of SBEI, SBEIIa and SBEIIb, and SSS of SSI and SSIII(or SSIIa), and DBE of isoamylase and pullulanase as well. In addition, among different crops even cultivars, genes encoding each enzyme may be distinct, eg, GBSS is controlled by Wx a and Wx b in indica and japonica rice respectively. Furthermore, the growing environmental can affect the expression level of a certain gene, regulated at transcriptional level. These genetic and environmental factors have resulted in various types of starches. With the rapid developments of transgenic technology and understanding of molecular biology of the starch biosynthesis, it becomes possible to artificially regulate starch synthesis. And thus opened a novel way to breeding of high quality cultivars and producing starches with new prosperities. This paper reviews the newest advancement on molecular biological researches of starch synthesis and improvement of the starch qualities by using transgenic technology, and at last, its prospects were discussed in this fascinating area.