pH Response Transcription Factor PacC Controls Salt Stress Tolerance and Expression of the P-Type Na + -ATPase Ena1 in Fusarium oxysporum

Abstract

ABSTRACT Fungi possess efficient mechanisms of pH and ion homeostasis, allowing them to grow over a wide range of environmental conditions. In this study, we addressed the role of the pH response transcription factor PacC in salt tolerance of the vascular wilt pathogen Fusarium oxysporum . Loss-of-function pacC +/− mutants showed increased sensitivity to Li + and Na + and accumulated higher levels of these cations than the wild type. In contrast, strains expressing a dominant activating pacC c allele were more salt tolerant and had lower intracellular Li + and Na + concentrations. Although the kinetics of Li + influx were not altered by mutations in pacC , we found that Li + efflux at an alkaline, but not at an acidic, ambient pH was significantly reduced in pacC +/− loss-of-function mutants. To explore the presence of a PacC-dependent efflux mechanism in F. oxysporum , we cloned ena1 encoding an orthologue of the yeast P-type Na + -ATPase ENA1. Northern analysis revealed that efficient transcriptional activation of ena1 in F. oxysporum required the presence of high Na + concentrations and alkaline ambient pH and was dependent on PacC function. We propose a model in which PacC controls ion homeostasis in F. oxysporum at a high pH by activating expression of ena1 coordinately with a second Na + -responsive signaling pathway.