GEF14 acts as a specific activator of the plant osmotic signaling pathway by controlling ROP6 nanodomain formation.

During their growth, plants encounter and respond to a variety of environmental signals. However, the mechanisms underlying the integration and specificity of signals remain poorly understood. Rho of Plant (ROP) signaling plays a central role in various processes, including polar cell growth and responses to different stimuli, and relies on stimuli-dependent membrane nanodomains. The effector composition of ROP6 nanodomains varies depending on the signal and may be involved in downstream signal specificity. In this study, we explore how ROP6 signaling is regulated by Guanine nucleotide Exchange Factor (GEF) during osmotic stress. We find that GEF14 is required for osmotically induced ROS accumulation. This isoform acts specifically in response to osmotic stimulation, since it is dispensable for other stimuli. We demonstrate that GEF14 activates ROP6 and controls its clustering in a signal-specific manner. Furthermore, we find that GEF14 relocates from the cytoplasm to clusters at the plasma membrane after osmotic stimulation. Together, our results suggest that a single GEF isoform can encode for signal specificity controlling ROP6 activation, clustering and downstream cellular responses.