CSIRO Agriculture and Food, GPO Box 1700, Canberra, ACT, 2601, Australia.
Research School of Biology, Australian National University, Canberra, ACT, 0200, Australia.
Theor Appl Genet. 2020 Oct;133(10):2961-2974. doi: 10.1007/s00122-020-03649-2. Epub 2020 Jul 10.
Catalytically active indica SSIIa allele in high amylose rice with down-regulated japonica SBEIIb can increase starch content and modify the starch structure and properties without changing its amylose content. Rice (Oryza sativa) genotypes with inactive starch synthase IIa (SSIIa) with recessive variants of starch branching enzyme IIb (SBEIIb) exhibit a range of alterations in grain phenotype, starch granule morphology, starch granule bound proteins, starch structure, and functional properties. However, the interactions between the two enzymes have not been thoroughly investigated yet. We analysed recombinant rice lines having down-regulated SBEIIb expression (SBEIIb) with either indica or japonica type SSIIa (SSIIa or SSIIa). In SBEIIb rice starch granules, the increased abundance of two protein bands (SSI and SSIIa) was found with eight additional protein bands not generally associated with starch granules. The amount of SSIIa was higher in SSIIaSBEIIb than SSIIaSBEIIb, which indicated that indica type SSIIa, possibly in the monomer form, was extensively involved in starch biosynthesis in the SBEIIb endosperm. Furthermore, SSIIaSBEIIb grains had higher total starch content and higher starch swelling power than SSIIaSBEIIb lines, but the amylopectin gelatinization temperatures and enthalpy and the apparent amylose content remained similar. In summary, this work suggests that SSIIa can partly compensate for the alteration of starch synthesis resulting from the SBEIIb down-regulation in japonica background without reducing its amylose content. The study provides insight into the starch structural and textural improvements of high amylose starch.
具有下调的粳稻 SBEIIb 的高直链淀粉水稻中催化活性的 indica SSIIa 等位基因可以增加淀粉含量并改变淀粉结构和性质，而不改变其直链淀粉含量。具有不活跃淀粉合酶 IIa（SSIIa）隐性变体的淀粉分支酶 IIb（SBEIIb）的水稻基因型表现出一系列谷物表型、淀粉颗粒形态、淀粉颗粒结合蛋白、淀粉结构和功能特性的改变。然而，这两种酶之间的相互作用尚未得到彻底研究。我们分析了具有下调的 SBEIIb 表达（SBEIIb）的重组水稻系，这些水稻系具有 indica 或粳稻类型的 SSIIa（SSIIa 或 SSIIa）。在 SBEIIb 水稻淀粉颗粒中，发现两个蛋白带（SSI 和 SSIIa）的丰度增加，还有八个通常与淀粉颗粒无关的额外蛋白带。SSIIaSBEIIb 中的 SSIIa 含量高于 SSIIaSBEIIb，这表明 indica 类型的 SSIIa 可能以单体形式广泛参与 SBEIIb 胚乳中的淀粉生物合成。此外，SSIIaSBEIIb 颗粒的总淀粉含量和淀粉膨胀力高于 SSIIaSBEIIb 系，但支链淀粉的糊化温度和焓以及表观直链淀粉含量保持相似。总之，这项工作表明，在不降低其直链淀粉含量的情况下，SSIIa 可以部分补偿由于 SBEIIb 下调而导致的淀粉合成的改变。该研究为高直链淀粉淀粉的淀粉结构和质构改进提供了新的见解。
