Ida Tamami, Crofts Naoko, Miura Satoko, Matsushima Ryo, Fujita Naoko
1 Laboratory of Plant Physiology, Department of Biological Production, Faculty of Bioresource Sciences, Akita Prefectural University.
2 Institute of Plant Science and Resources, Okayama University.
J Appl Glycosci (1999). 2021 Apr 30;68(2):31-39. doi: 10.5458/jag.jag.JAG-2021_0002. eCollection 2021.
Starch biosynthetic enzymes form multi-protein complexes consisting of starch synthase (SS) I, SSIIa, and starch branching enzyme (BE) IIb, which synthesize amylopectin clusters. This study analyzed the starch properties in two double mutant rice lines lacking SSIIa and BEIIb, one of which expressed an inactive BEIIb protein. The lines showed similar or greater seed weight than the lines, and plant growth was not affected. The line showed increased short amylopectin chains resulting in a lower gelatinization temperature. Starch granule morphology and A-type crystallinity were similar between the line and the wild type, except for a mild chalky seed phenotype in the line. However, the starch phenotype of the lines, which was similar to that of but not , was characterized by increased long amylopectin chains, abnormal starch granules, and B-type crystallinity. The similarity in phenotype between the and lines may be attributed to the inability of the mutants to generate short amylopectin branches, which serve as primers for SSIIa. Therefore, the presence or absence of SSIIa hardly affected the amylopectin structure under the background. The amylose content was significantly higher in the lines than in the lines. Starch crystallinity was greater in lines than in lines, despite the fact that starch crystallinity is generally negatively correlated with amylose content. This suggests that the formation of a double helix between long amylopectin chains and amylose affects starch crystallinity in the mutants.
淀粉生物合成酶形成由淀粉合酶（SS）I、SSIIa和淀粉分支酶（BE）IIb组成的多蛋白复合物，这些复合物合成支链淀粉簇。本研究分析了两个缺失SSIIa和BEIIb的双突变水稻品系的淀粉特性，其中一个品系表达无活性的BEIIb蛋白。这些品系的种子重量与对照品系相似或更高，且植株生长未受影响。缺失BEIIb的品系短支链淀粉链增加，导致糊化温度降低。除了缺失BEIIb的品系有轻度垩白种子表型外，该品系与野生型之间的淀粉颗粒形态和A型结晶度相似。然而，同时缺失SSIIa和BEIIb的品系的淀粉表型与仅缺失BEIIb的品系相似，而与野生型不同，其特征是长支链淀粉链增加、淀粉颗粒异常和B型结晶度。缺失SSIIa和BEIIb的品系与仅缺失BEIIb的品系在表型上的相似性可能归因于缺失SSIIa的突变体无法产生作为SSIIa引物的短支链淀粉分支。因此，在缺失BEIIb的背景下，SSIIa的存在与否对支链淀粉结构几乎没有影响。缺失SSIIa和BEIIb的品系的直链淀粉含量显著高于仅缺失BEIIb的品系。尽管淀粉结晶度通常与直链淀粉含量呈负相关，但缺失SSIIa和BEIIb的品系的淀粉结晶度高于仅缺失BEIIb的品系。这表明长支链淀粉链和直链淀粉之间双螺旋的形成影响了缺失SSIIa和BEIIb的突变体中的淀粉结晶度。
