C2-domain abscisic acid-related proteins regulate the dynamics of a plasma membrane H⁺-ATPase in response to alkali stress.

This article investigates the regulatory role of C2-domain abscisic acid-related (CAR) proteins on the plasma membrane H+- ATPase AHA1 in Arabidopsis thaliana during plant responses to alkali stress. The study demonstrates that multiple CAR family members physically interact with AHA1 at the plasma membrane, and that triple mutants lacking CAR1, CAR6, and CAR10 exhibit enhanced tolerance to alkaline conditions through increased proton extrusion mediated by AHA1. Using variable-angle total internal reflection fluorescence microscopy and single-particle tracking, the authors reveal that alkali stress increases the lateral mobility and reduces the membrane residence time of AHA1, effects that are further enhanced in the absence of CAR proteins. These findings suggest that CAR proteins act as negative regulators of AHA1 dynamics and activity, thereby modulating plant adaptation to high-pH stress by influencing proton pump behavior at the single-molecule level.