A Munc13-like protein in Arabidopsis mediates H⁺-ATPase translocation that is essential for stomatal responses

Plants control CO₂ uptake and water loss by modulating the aperture of stomata located in the epidermis. Stomatal opening is initiated by the activation of H +-ATPases in the guard-cell plasma membrane. In contrast to regulation of H +-ATPase activity, little is known about the translocation of the guard cell H +-ATPase to the plasma membrane. Here we describe the isolation of an Arabidopsis gene, PATROL1, that controls the translocation of a major H +-ATPase, AHA1, to the plasma membrane. PATROL1 encodes a protein with a MUN domain, known to mediate synaptic priming in neuronal exocytosis in animals. Environmental stimuli change the localization of plasma membrane-associated PATROL1 to an intracellular compartment. Plasma membrane localization of AHA1 and stomatal opening require the association of PATROL1 with AHA1. Increased stomatal opening responses in plants overexpressing PATROL1 enhance the CO 2 assimilation rate, promoting plant growth.