Haigang Yan, Wenwei Zhang, Yihua Wang, Jie Jin, Hancong Xu, Yushuang Fu, Zhuangzhuang Shan, Xin Wang, Xuan Teng, Xin Li, Yongxiang Wang, Xiaoqing Hu, Wenxiang Zhang, Changyuan Zhu, Xiao Zhang, Yu Zhang, Rongqi Wang, Jie Zhang, Yue Cai, Xiaoman You, Jie Chen, Xinyuan Ge, Liang Wang, Jiahuan Xu, Ling Jiang, Shijia Liu, Cailin Lei, Xin Zhang, Haiyang Wang, Yulong Ren, Jianmin Wan

The Plant Cell; 2024; IF 11.6

DOI:10.1093/plcell/koae006

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 ISOAMYLASE 1 (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.