Spatial regulation of RBOHD via AtECA4-mediated recycling and clathrin-mediated endocytosis contributes to ROS accumulation during salt stress response but not flg22-induced immune response.

Abstract

Various environmental stresses can induce production of reactive oxygen species (ROS) to turn on signaling for proper responses to those stresses. Plasma membrane (PM)-localized respiratory burst oxidase homologs (RBOHs), in particular RBOHD, produce ROS via the post-translational activation upon abiotic and biotic stresses. Although the mechanisms of RBOHD activation upon biotic stress have been elucidated in detail, it remains elusive how salinity stress activates RBOHD. Here, we present evidence that trafficking of PM-localized RBOHD to endosomes and then its recycling back to the PM is critical for ROS accumulation upon salinity stress. ateca4 plants that were defective in recycling of proteins from endosomes to the PM and clc2-1 and chc2-1 plants that were defective in endocytosis showed a defect in salinity stress-induced ROS production. In addition, ateca4 plants showed a defect in transient accumulation of GFP:RBOHD to the PM at the early stage of salinity stress. By contrast, ateca4 plants showed no defect in the increase in the ROS level and accumulation of RBOHD to the PM upon flg22 treatment as wild-type plants. Based on these observations, we propose that factors involved in the trafficking machinery such as AtECA4 and clathrin are important players in salt stress-induced, but not flg22-induced, ROS accumulation.