The evolution of plant proton pump regulation via the R domain may have facilitated plant terrestrialization.

Plasma membrane (PM) H-ATPases are the electrogenic proton pumps that export H from plant and fungal cells to acidify the surroundings and generate a membrane potential. Plant PM H-ATPases are equipped with a C‑terminal autoinhibitory regulatory (R) domain of about 100 amino acid residues, which could not be identified in the PM H-ATPases of green algae but appeared fully developed in immediate streptophyte algal predecessors of land plants. To explore the physiological significance of this domain, we created in vivo C-terminal truncations of autoinhibited PM H‑ATPase2 (AHA2), one of the two major isoforms in the land plant Arabidopsis thaliana.