Phytophthora nicotianae PnPMA1 encodes an atypical plasma membrane H+-ATPase that is functional in yeast and developmentally regulated

PnPMA1, a gene encoding a putative P-type plasma membrane H+-ATPase, has been isolated by differential screening of a Phytophthora nicotianae germinated cyst cDNA library. PnPMA1 is differentially expressed during pathogen asexual development with a more than 10-fold increase in expression in germinated cysts, the stage at which plant infection is initiated, compared to vegetative or sporulating hyphae or motile zoospores. PnPMA1 proteins are encoded by two closely linked genes that have no introns and encode identical proteins having 1068 amino acid residues and a molecular mass of 116.3 kDa. PnPMA1 shows moderate identity (30–50%) to plant and fungal plasma membrane H+-ATPases and weak identity to other P-type cation-transporting ATPases. PnPMA1 contains all the catalytic domains characteristic of H+-ATPases but also has a distinct domain of ∼155 amino acids that forms a putative cytoplasmic loop between transmembrane domains 8 and 9, a feature that is not present in PMA1 proteins from other organisms. Polyclonal antibodies raised against the 155 residue domain were shown by immunogold labelling to react with a protein in the plasma membrane of P. nicotianae germinated cysts but not with the plasma membrane of motile zoospores. Genetic complementation experiments demonstrated that the P. nicotianae PnPMA1 is functional in yeast, Saccharomyces cerevisiae.