Role of ENA ATPase in Na+ efflux at high pH in bryophytes

Potassium or Na+ efflux ATPases, ENA ATPases, are present in all fungi and play a central role in Na+ efflux and Na+ tolerance. Flowering plants lack ENA ATPases but two ENA ATPases have been identified in the moss Physcomitrella patens, PpENA1 and PpENA2. PpENA1 mediates Na+ efflux in Saccharomyces cerevisiae. To propose a general function of ENA ATPases in bryophytes it was necessary to demonstrate that these ATPases mediate Na+ efflux in planta and that they exist in more bryophytes than P. patens. For these demonstrations (1) we cloned a third ATPase from P. patens, PpENA3, and studied the expression pattern of the three PpENA genes; (2) we constructed and studied the single and double Delta ppena1 and Delta ppena2 mutants; and (3) we cloned two ENA ATPases from the liverwort Marchantia polymorpha, MpENA1 and MpENA2, and expressed them in S. cerevisiae. The results from the first two approaches revealed that the expression of ENA ATPases was greatly enhanced at high pH and that Na+ efflux at high pH depended on PpENA1. The ENA1 ATPase of M. polymorpha suppressed the defective growth of a S. cerevisiae mutant at high K+ or Na+ concentrations, especially at high K+.