The 14-3-3 protein interacts directly with the C-terminal region of the plant plasma membrane H+-ATPase

Accumulating evidence suggests that 14-3-3 proteins are involved in the regulation of plant plasma membrane H+-ATPase activity. However, it is not known whether the 14-3-3 protein interacts directly or indirectly with the H+-ATPase. In this study, detergent-solubilized plasma membrane H+-ATPase isolated from fusicoccin-treated maize shoots was copurified with the 14-3-3 protein (as determined by protein gel blotting), and the H+-ATPase was recovered in an activated state, In the absence of fusicoccin treatment, H+-ATPase and the 14-3-3 protein were well separated, and the H+-ATPase was recovered in a nonactivated form, Trypsin treatment removed the 10-kD C-terminal region from the H+-ATPase as well as the 14-3-3 protein, Using the yeast two-hybrid system, we could show a direct interaction between Arabidopsis 14-3-3 GF14-phi and the last 98 C-terminal amino acids of the Arabidopsis AHA2 plasma membrane H+-ATPase, We propose that the 14-3-3 protein is a natural ligand of the plasma membrane H+-ATPase, regulating proton pumping by displacing the C-terminal autoinhibitory domain of the H+-ATPase.