title: Rice actin-binding protein RMD is a key link in the auxin-actin regulatory loop that controls cell growth.
abstract: The plant hormone auxin plays a central role in plant growth and development. Auxin transport and signaling depend on actin organization. Despite its functional importance, the mechanistic link between actin filaments (F-actin) and auxin intracellular signaling remains unclear. Here, we report that the actin-organizing protein Rice Morphology Determinant (RMD), a type II formin from rice (Oryza sativa), provides a key link. Mutants lacking RMD display abnormal cell growth and altered configuration of F-actin array direction. The rmd mutants also exhibit an inhibition of auxin-mediated cell elongation, decreased polar auxin transport, altered auxin distribution gradients in root tips, and suppression of plasma membrane localization of auxin transporters O. sativa PIN-FORMED 1b (OsPIN1b) and OsPIN2 in root cells. We demonstrate that RMD is required for endocytosis, exocytosis, and auxin-mediated OsPIN2 recycling to the plasma membrane. Moreover, RMD expression is directly regulated by heterodimerized O. sativa auxin response factor 23 (OsARF23) and OsARF24, providing evidence that auxin modulates the orientation of F-actin arrays through RMD. In support of this regulatory loop, osarf23 and lines with reduced expression of both OsARF23 and OsARF24 display reduced RMD expression, disrupted F-actin organization and cell growth, less sensitivity to auxin response, and altered auxin distribution and OsPIN localization. Our findings establish RMD as a crucial component of the auxin-actin self-organizing regulatory loop from the nucleus to cytoplasm that controls rice cell growth and morphogenesis.
authors: State Key Laboratory of Hybrid Rice, Shanghai Jiao Tong University-University of Adelaide Joint Centre for Agriculture and Health, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 20040, China;
authors: Gang
authors: G
authors: Li
authors: State Key Laboratory of Hybrid Rice, Shanghai Jiao Tong University-University of Adelaide Joint Centre for Agriculture and Health, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 20040, China;
authors: Wanqi
authors: W
authors: Liang
authors: State Key Laboratory of Hybrid Rice, Shanghai Jiao Tong University-University of Adelaide Joint Centre for Agriculture and Health, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 20040, China;
authors: Xiaoqing
authors: X
authors: Zhang
authors: Key Laboratory of Cell Proliferation and Regulation Biology of the Ministry of Education, College of Life Science, Beijing Normal University, Beijing 100875, China;
authors: Haiyun
authors: H
authors: Ren
authors: Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824;
authors: Jianping
authors: J
authors: Hu
authors: Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, United Kingdom; andCollege of Science, King Saud University, Riyadh 11451, Kingdom of Saudi Arabia.
authors: Malcolm J
authors: MJ
authors: Bennett
authors: State Key Laboratory of Hybrid Rice, Shanghai Jiao Tong University-University of Adelaide Joint Centre for Agriculture and Health, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 20040, China; zhangdb@sjtu.edu.cn.
authors: Dabing
authors: D
authors: Zhang
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism*; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D012275:Oryza / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D008840:Microfilament Proteins; D010940:Plant Proteins
keywords: actin cytoskeleton; auxin signaling; rice morphogenesis