Summary

Abstract

Summary: The plasma membrane H+‐ATPase in higher plants has been implicated in nutrient uptake, phloem loading, elongation growth and establishment of turgor. Although a C‐terminal regulatory domain has been identified, little is known about the physiological factors involved in controlling the activity of the enzyme. To identify components which play a role in the regulation of the plant H+‐ATPase, a fusicoccin responsive yeast expressing Arabidopsis plasma membrane H+‐ATPase AHA2 was employed. By testing the fusicoccin binding activity of yeast membranes, the C‐terminal regulatory domain of AHA2 was found to be part of a functional fusicoccin receptor, a component of which was the 14–3‐3 protein. ATP hydrolytic activity of AHA2 expressed in yeast internal membranes was activated by all tested isoforms of the 14–3‐3 protein of yeast and Arabidopsis, but only in the presence of fusicoccin, and activation was prevented by a phosphoserine peptide representing a known 14–3‐3 protein binding motif in Raf‐1. The results demonstrate that the 14–3‐3 protein is an activator molecule of the H+‐ATPase and provides the first evidence of a protein involved in activation of plant plasma membrane H+‐ATPase.