PDF(Pubmed)
Abstract：
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.
摘要：
在谷物中，淀粉是通过多种酶在淀粉体内淀粉颗粒表面的协同作用合成的。然而,对淀粉合成酶如何进入淀粉颗粒知之甚少，特别是支链淀粉的生物合成。这里,我们表明，水稻（Oryzasativa）面粉胚乳9（flo9）突变体在支链淀粉的生物合成中存在缺陷，导致谷物表现出带有空心核的粉质胚乳。分子克隆显示，FLO9编码与拟南芥（拟南芥）同源的植物特异性蛋白质，如早期STARVATION1（LESV）。与拟南芥LESV不同，参与叶片中的淀粉代谢，胚乳中淀粉颗粒的起始需要OsLESV。OsLESV可以通过其富含C端色氨酸(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，并且任一基因的功能丧失突变都会削弱异淀粉酶1（ISA1）靶向淀粉颗粒。基因上,OsLESV与FLO6协同作用调节淀粉生物合成和胚乳发育。一起,我们的结果确定OsLESV-FLO6是负责淀粉颗粒上ISA1定位的非酶分子模块，并提出了用于生物技术控制水稻胚乳中淀粉含量和组成的靶基因。
