Rice glutamate receptor-like channel OsGLR3.4 modulates the root tropism growth towards amino acids via plasma membrane depolarization and ROS generation

Understanding how plants determine root directional growth towards nutrient sources is important to reveal optimal strategies during plant growth. GLUTAMATE RECEPTOR-LIKE (GLR) channels play essential roles in various Ca2+-mediated plant-specific physiological processes, but how GLRs are involved in the root tropism growth towards surrounding nutrients remains largely unknown. Here, we report that OsGLR3.4, a rice Ca2+-permeable channel, specifically modulates the root growth and tropism towards Glycine (Gly) via Ca2+-mediated electrical activity and reactive oxygen species (ROS) production. Mutation of OsGLR3.4 significantly reduced the inhibitory effect of Gly on the primary root growth, coupled with the decrease of Gly-induced membrane depolarization and ROS levels at the elongation zone in the root tip. More importantly, our results showed that OsGLR3.4 was required for root nutritropism growth towards Gly. Mechanistic study showed that, when grown in the agar with unequal Gly application, the bilaterally asymmetrical distribution of membrane depolarization and ROS evoked by OsGLR3.4-mediated [Ca2+]cyt fluctuation across the root resulted in the differential cell elongation at two sides of the root tip, which therefore led to the root nutritropism growth. Nevertheless, addition of Ca2+ channel blocker eliminated the Gly-induced asymmetrical distribution of depolarization and ROS across the root tip. Notably, OsGLR3.4 promoted the nitrate uptake in the root by enhancing expression of nitrate transporter genes in response to Gly treatment, suggesting its potential roles in crop yield. Our findings established a mechanism by which OsGLR3.4 modulates rice root growth and tropism towards nutrient sources, and shed light on the root behavioral property used by plants to acquire nutrients efficiently.