Characterization of StPPI1, a proton pump interactor from Solanum tuberosum L. that is up-regulated during tuber development and by abiotic stress.

Plasma membrane proton pumps (PM H(+)-ATPases) are involved in several physiological processes, such as growth and development, and abiotic stress responses. The major regulators of the PM H(+)-ATPases are proteins of the 14-3-3 family, which stimulate its activity. In addition, a novel interaction partner of the AHA1 PM H(+)-ATPase, named PPI1 (proton pump interactor, isoform 1), was identified in Arabidopsis thaliana. This protein stimulates the activity of the proton pump in vitro. In this work, we report the characterization of an A. thaliana PPI1 homolog in potato (Solanum tuberosum L.) named StPPI1. The full-length coding sequence of StPPI1 was obtained. The open reading frame (ORF) encodes a protein of 629 amino acids showing 50% identity with A. thaliana PPI1 protein. The StPPI1 ORF is divided into seven exons split by six introns. Southern blot analysis suggests that StPPI1 belongs to a family of related genes. Recombinant StPPI1 stimulates H(+)-ATPase activity in vitro. Basal levels of StPPI1 transcripts are observed in all tissues, however, StPPI1 expression is higher in proliferative regions (shoot apex and flower buds), flowers and leaves than in shoots and roots. StPPI1 mRNA levels significantly increase during tuber development. StPPI1 is induced by salt stress and cold. Drought and mechanical wounding slightly increase StPPI1 transcript levels. In addition, the expression of SlPPI1, the tomato homolog of StPPI1, was determined under adverse environmental conditions in tomato plants. SlPPI1 mRNA levels are increased by drought and cold, but are unaffected by salt stress. Mechanical wounding slightly increases SlPPI1 expression.