Rice roots avoid asymmetric heavy metal and salinity stress via a RBOH-ROS-auxin signaling cascade
H. Q. Wang, X. Y. Zhao, W. Xuan and F. J. Zhao
State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China

Root developmental plasticity is critical for plants to adapt to changing soil environment, where nutrients and abiotic stress factors are distributed heterogeneously. How plant roots sense and avoid heterogeneous abiotic stress in soil remains unclear. Here, we show that, in response to asymmetric stress of heavy metals (Cd, Cu or Pb) and salt (NaCl), rice roots rapidly proliferate lateral root branching in the stress-free area, thereby remodeling root architecture to avoid localized stress. Imaging and quantitative analyses of reactive oxygen species (ROS) show that asymmetric stress induces ROS burst in the tips of the exposed roots, simultaneously triggering rapid systemic ROS signaling to the unexposed roots, which is prerequisite to stress-induced lateral root branching. We identify two respiratory burst oxidase homologs, OsRBOHA and OsRBOHI, as key players for ROS generation and systemic signaling in response to asymmetric stress. Auxin signaling and cell wall remodeling act downstream of the systemic ROS signaling to promote lateral root development. Our study reveals a RBOH-ROS-auxin signaling cascade that enables rice roots to avoid localized stress of heavy metals and salt and provides new insight into root system plasticity in heterogenous soil.