Inactivation of rice starch branching enzyme IIb triggers broad and unexpected changes in metabolism by transcriptional reprogramming
Inactivation of rice starch branching enzyme IIb triggers broad and unexpected changes in metabolism by transcriptional reprogramming
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DOI：
10.1073/pnas.2014860117
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发表时间：
2020-10-20
影响因子：
11.1
通讯作者：
Christou, Paul
中科院分区：
文献类型：
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作者：
Baysal, Can;He, Wenshu;Christou, Paul
淀粉的性质可以通过突变胚乳中负责合成直链淀粉和支链淀粉的基因来改变。然而，很少有人知道这种有针对性的修改对整个淀粉生物合成途径和更广泛的代谢的影响。在这里，我们研究了突变OsSBEIIb基因编码淀粉分支酶IIb，这是必需的支链淀粉在胚乳中的合成的影响。正如预期的那样，纯合突变体植物，其中OsSBEIIb是完全失活的废除催化中心和C-末端调控结构域，产生不透明的种子耗尽淀粉储备。直链淀粉含量从19.6%提高到27.4%，抗性淀粉含量从0.2%提高到17.2%。许多基因编码亚型的AGR 1，可溶性淀粉合成酶，和其他淀粉分支酶的上调，无论是在其天然组织或在异位的方式，而基因编码颗粒结合淀粉合成酶，脱支酶，支链淀粉酶，淀粉磷酸化酶在很大程度上下调。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产物通过溢出途径增加通量，对多种初级和次级代谢产物的积累产生深远影响。我们的研究结果提供了更广泛的影响，扰乱淀粉代谢在水稻胚乳及其对整个植物的影响，这将使它更容易预测谷物的营养改善或有价值的代谢产物的生产代谢工程的影响的见解。
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.