The rice actin-binding protein RMD regulates light-dependent shoot gravitropism

First author: Yu Song; Affiliations: Shanghai Jiao Tong University (上海交通大学): Shanghai, China

Corresponding author: Dabing Zhang

Light and gravity are two key determinants in orientating plant stems for proper growth and development. The organization and dynamics of the actin cytoskeleton are essential for cell biology and critically regulated by actin-binding proteins. However, the role of actin cytoskeleton in shoot negative gravitropism remains controversial. In this work, we report that the actin-binding protein Rice Morphology Determinant (RMD) promotes re-organization of the actin cytoskeleton in rice (Oryza sativaL.) shoots. The changes in actin organization associated with the ability of the rice shoots to respond to negative gravitropism. Here, light-grown rmdmutant shoots exhibited agravitropic (无向重力的) phenotypes. By contrast, etiolated rmd shoots displayed normal negative shoot gravitropism. Furthermore, we show that RMD maintains an actin configuration that promotes statolith (平衡) mobility in gravisensing endodermal cells, and for proper auxin distribution in light-grown, but not dark-grown, shoots. RMD gene expression is diurnally controlled and directly repressed by the phytochrome-interacting factor-like protein OsPIL16. Consequently, over-expression of OsPIL16 led to gravisensing and actin patterning defects that phenocopied the rmd mutant. Our findings outline a mechanism that links light signaling and gravity perception for straight shoot growth in rice.

光照和重力是两个决定植物茎生长方向的关键因素，这对于植物的正确生长和发育非常重要。肌动蛋白细胞骨架的组织和动态对于细胞生物学是必需的，该过程受到肌动蛋白结合蛋白的调控。然而， 肌动蛋白细胞骨架在植物地上部分的反重力方向生长过程中所发挥的作用还不清楚。本文中，作者报道了肌动蛋白结合蛋白水稻形态决定因子RMD促进水稻地上部分组织中的肌动蛋白细胞骨架重组。肌动蛋白组织上的变化与水稻地上部分响应负重力方向生长的能力相关。生长下光下的水稻rmd突变体，其地上部分存在无向重力性表型。而相反，黄化的rmd突变体地上部分则显示出正常的负重力方向生长。此外，作者的研究显示RMD维持一个肌动蛋白配置，促进感受重力的内皮层细胞的平衡流动，保证光下生长的地上组织中正确的生长素分布。RMD基因在日间表达，并且受到类光敏色素相互作用因子蛋白OsPIL16的直接抑制。过表达OsPIL16基因能够导致与rmd突变体类似的重力感应与肌动蛋白模式的缺陷。本文的研究揭示了一个光照信号与重力感知相互关联的分子机制，其共同作用于水稻的茎向上径直生长。

通讯：张大兵  (http://life.sjtu.edu.cn/Data/View/354)

个人简介：1991-1994年，南京大学，学士；1994-1998年，中国科学院上海植物生理生态研究所，博士 。

研究方向：水稻花器官形态建成的分子调控机理研究；水稻雄性生殖发育的分子调控机制研究；水稻分子辅助育种。

doi: https://doi.org/10.1104/pp.19.00497

Journal: Plant Physiology

Published date: August 15, 2019