Intracellular localisation of PPI1 (proton pump interactor, isoform 1), a regulatory protein of the plasma membrane H+-ATPase of Arabidopsis thaliana

PPI1 (proton pump interactor isoform 1) is a novel protein able to interact with the C-terminal autoinhibitory domain of the Arabidopsis thaliana plasma membrane (PM) H⁺-ATPase. In vitro, PPI1 binds the PM H⁺-ATPase in a site different from the known 14-3-3 binding site and stimulates its activity. In this study, we analysed the intracellular localisation of PPI1. The intracellular distribution was monitored in A. thaliana cultured cells by immunolocalisation using an antiserum against the PPI1 N-terminus and in Vicia faba guard cells and epidermal cells by transient expression of a GFP::PPI1 fusion. The results indicate that the bulk of PPI1 is localised at the endoplasmic reticulum, from which it might be recruited to the PM for interaction with the H⁺-ATPase in response to as yet unidentified signals.