Starch properties can be modified by mutating genes responsible for the synthesis of amylose and amylopectin in the endosperm. However, little is known about the effects of such targeted modifications on the overall starch biosynthesis pathway and broader metabolism. Here we investigated the effects of mutating the OsSBEIIb gene encoding starch branching enzyme IIb, which is required for amylopectin synthesis in the endosperm. As anticipated, homozygous mutant plants, in which OsSBEIIb was completely inactivated by abolishing the catalytic center and C-terminal regulatory domain, produced opaque seeds with depleted starch reserves. Amylose content in the mutant increased from 19.6 to 27.4% and resistant starch (RS) content increased from 0.2 to 17.2%. Many genes encoding isoforms of AGPase, soluble starch synthase, and other starch branching enzymes were up-regulated, either in their native tissues or in an ectopic manner, whereas genes encoding granule-bound starch synthase, debranching enzymes, pullulanase, and starch phosphorylases were largely down-regulated. There was a general increase in the accumulation of sugars, fatty acids, amino acids, and phytosterols in the mutant endosperm, suggesting that intermediates in the starch biosynthesis pathway increased flux through spillover pathways causing a profound impact on the accumulation of multiple primary and secondary metabolites. Our results provide insights into the broader implications of perturbing starch metabolism in rice endosperm and its impact on the whole plant, which will make it easier to predict the effect of metabolic engineering in cereals for nutritional improvement or the production of valuable metabolites.

可以通过突变负责胚乳中直链淀粉和支链淀粉合成的基因来改变淀粉特性。然而，人们对这种有针对性的修饰对整个淀粉生物合成途径和更广泛的代谢的影响知之甚少。在这里，我们研究了编码淀粉分支酶 IIb 的OsSBEIIb基因突变的影响，该酶是胚乳中支链淀粉合成所必需的。正如预期的那样，纯合突变植物（其中 OsSBEIIb 通过废除催化中心和 C 末端调节结构域而完全失活）产生了淀粉储备耗尽的不透明种子。突变体中的直链淀粉含量从19.6%增加到27.4%，抗性淀粉(RS)含量从0.2%增加到17.2%。许多编码 AGP 酶、可溶性淀粉合酶和其他淀粉分支酶亚型的基因在其天然组织中或以异位方式上调，而编码颗粒结合淀粉合酶、脱支酶、普鲁兰酶和淀粉磷酸化酶的基因则被上调。大幅下调。突变体胚乳中糖、脂肪酸、氨基酸和植物甾醇的积累普遍增加，表明淀粉生物合成途径中的中间体增加了溢出途径的通量，对多种初级和次级代谢物的积累产生了深远的影响。我们的研究结果提供了对水稻胚乳中淀粉代谢扰动的更广泛影响及其对整个植物的影响的见解，这将使得更容易预测谷物中代谢工程对营养改善或有价值代谢物生产的影响。