Genetic modification of amylopectin fine structure in endosperm starch of rice

我们通过MNU处理获得了1200多个修饰支链淀粉精细结构的新突变体。支链淀粉合成过程中至少有10种独立酶参与，分别为5种SSS酶、3种BE酶和2种DBE酶。分离到支链淀粉生物合成相关酶编码基因的突变，BE IIb突变显著减少了dp17以下的短链，增加了DP19以上的长链。相反，BE I突变体支链淀粉表现为DP值大于38的长链显著减少，DP值在12 ~ 23之间的短链显著减少，而小于DP12的短链显著增加。BE - 1突变体胚乳淀粉的热糊化起始温度较低。相比之下，BE IIb突变体表现出更高的热糊化起始温度。这些结果表明，支链淀粉精细结构的遗传修饰是导致淀粉理化性质和流变性质的主要原因。这些结果支持了支链淀粉结构的改变，特别是在簇内的短链，可能在淀粉的流变性能中起关键作用的观点。因此，对BEs基因进行基因改造可能会合成新型淀粉，作为食品和淀粉工业的新材料。ISA缺陷突变显著增加了短链，减少了长链。与野生型相比，DBE突变体的流变特性具有极低的粘度。SS突变改变了支链淀粉的精细结构和流变性能，BE和DBE突变也改变了支链淀粉的流变性能。这些结果表明，支链淀粉的精细结构在确定淀粉的流变性能中起着重要的作用，而基因改造将导致水稻新型淀粉的产生。

We obtained newly more than 1,200 mutants modifying amylopectin fine structure by MNU treatment. At least 10 independent enzymes were participated in amylopectin biosynthesis, those are, 5 kinds of SSS, 3 of BE and 2 of DBE. The mutations of genes encoding respective enzymes involved in amylopectin biosynthesis were isolated,BE IIb mutation decreased specifically the short chains with less than DP 17 and increased longer chains with more than DP19. Contrarily, the amylopectin of BE I mutant was characterized by the significant decrease in long chains with more than DP 38 and the short chains with DP 12 to 23, and marked increase in short chains with less than DP12. The endosperm starch from the BE I mutant had the lower onset temperature for thermo-gelatinization. By contrast, BE IIb mutant showed the higher onset temperature for thermo-gelatinization. These findings indicate that the genetic modification of amylopectin fine structure is responsible for changes in physicochemical and rheological properties of the starch. The results support the view that alterations in amylopectin structure, in particular in short chains within clusters, might play a critical role in the rheological properties of starch. It is, therefore, likely that genetic modification of the gene for BEs will lead to the synthesis of novel types of starch as new materials for the foods and starch industries. ISA deficient mutations increased the short chains and decreased long chains dramatically. Rheological properties of DBE mutant are characterized by extremely lower viscosity in contrast to that of wild type. SS mutations altered the fine structure of amylopectin and their rheological properties as well as BE and DBE mutations. These results imply that amylopectin fine structure is important in determination of rheological properties of starch and genetic modification lead to the development of novel starch in rice.