Overexpression of PeHA1 enhances hydrogen peroxide signaling in salt-stressed Arabidopsis

The plant plasma membrane (PM) H+-ATPase plays a crucial role in controlling K+/Na+ homeostasis under salt stress. Our previous microarray analysis indicated that Populus euphratica retained a higher abundance of PM H+-ATPase transcript versus a salt-sensitive poplar. To clarify the roles of the PM H+-ATPase in salt sensing and adaptation, we isolated the PM H+-ATPase gene PeHA1 from P. euphratica and introduced it into Arabidopsis thaliana. Compared to wild-type, PeHA1-transgenic Arabidopsis had a greater germination rate, root length, and biomass under NaCl stress (50–150 mM). Ectopic expression of PeHA1 remarkably enhanced the capacity to control the homeostasis of ions and reactive oxygen species in salinized Arabidopsis. Flux data from salinized roots showed that transgenic plants exhibited a more pronounced Na+/H+ antiport and less reduction of K+ influx versus wild-type. Enhanced PM ATP hydrolytic activity, proton pumping, and Na+/H+ antiport in PeHA1-transgenic plants, were consistent to those observed in vivo, i.e., H+ extrusion, external acidification, and Na+ efflux. Activities of the antioxidant enzymes ascorbate peroxidase and catalase were typically higher in transgenic seedlings irrespective of salt concentration. In transgenic Arabidopsis roots, H2O2 production was higher under control conditions and increased more rapidly than wild-type when plants were subjected to NaCl treatment. Interestingly, transgenic plants were unable to control K+/Na+ homeostasis when salt-induced H2O2 production was inhibited by diphenylene iodonium, an inhibitor of NADPH oxidase. These observations suggest that PeHA1 accelerates salt tolerance partially through rapid H2O2 production upon salt treatment, which triggers adjustments in K+/Na+ homeostasis and antioxidant defense in Arabidopsis.