Proton pump interactor, isoform 1 (PPI1) is a novel interactor of the C-ter-minus ofArabidopsis thalianaplasma membrane H + -ATPase (EC ) (Morandini P, Valera M, Albumi C, Bonza MC, Giacometti S, Ravera G, Murgia I, Soave C & De Michelis MI (2002)Plant J31,487–497).