State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, Nanjing Agricultural University, Nanjing 210095, China.
State Key Laboratory of Crop Gene Resources and Breeding, Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
Plant Cell. 2024 May 1;36(5):1892-1912. doi: 10.1093/plcell/koae006.
In cereal grains, starch is synthesized by the concerted actions of multiple enzymes on the surface of starch granules within the amyloplast. However, little is known about how starch-synthesizing enzymes access starch granules, especially for amylopectin biosynthesis. Here, we show that the rice (Oryza sativa) floury endosperm9 (flo9) mutant is defective in amylopectin biosynthesis, leading to grains exhibiting a floury endosperm with a hollow core. Molecular cloning revealed that FLO9 encodes a plant-specific protein homologous to Arabidopsis (Arabidopsis thaliana) LIKE EARLY STARVATION1 (LESV). Unlike Arabidopsis LESV, which is involved in starch metabolism in leaves, OsLESV is required for starch granule initiation in the endosperm. OsLESV can directly bind to starch by its C-terminal tryptophan (Trp)-rich region. Cellular and biochemical evidence suggests that OsLESV interacts with the starch-binding protein FLO6, and loss-of-function mutations of either gene impair ISOAMYLASE1 (ISA1) targeting to starch granules. Genetically, OsLESV acts synergistically with FLO6 to regulate starch biosynthesis and endosperm development. Together, our results identify OsLESV-FLO6 as a non-enzymatic molecular module responsible for ISA1 localization on starch granules, and present a target gene for use in biotechnology to control starch content and composition in rice endosperm.
在谷物中，淀粉是由多个酶在淀粉体中淀粉颗粒表面的协同作用下合成的。然而，对于淀粉合成酶如何接近淀粉颗粒，人们知之甚少，特别是对于支链淀粉的生物合成。在这里，我们展示了水稻粉质胚乳 9 号（flo9）突变体在支链淀粉生物合成中存在缺陷，导致其颗粒表现出粉质胚乳，中央有空腔。分子克隆表明，FLO9 编码一种与拟南芥（Arabidopsis thaliana）同源的植物特异性蛋白，类似于早期饥饿 1 号（LESV）。与参与叶片淀粉代谢的拟南芥 LESV 不同，OsLESV 是胚乳中淀粉颗粒起始所必需的。OsLESV 可以通过其 C 端富含色氨酸（Trp）的区域直接与淀粉结合。细胞和生化证据表明，OsLESV 与淀粉结合蛋白 FLO6 相互作用，并且这两个基因的功能丧失突变都会损害 ISOAMYLASE1（ISA1）向淀粉颗粒的靶向。从遗传角度来看，OsLESV 与 FLO6 协同作用，调节淀粉生物合成和胚乳发育。总之，我们的研究结果确定了 OsLESV-FLO6 作为一个非酶分子模块，负责 ISA1 在淀粉颗粒上的定位，并为生物技术提供了一个靶基因，用于控制水稻胚乳中淀粉的含量和组成。
