Populus euphratica J3 mediates root K + /Na + homeostasis by activating plasma membrane H + -ATPase in transgenic Arabidopsis under NaCl salinity

NaCl induced PeJ3 (a DnaJ homolog) expression in Populus euphratica cell cultures. In contrast, salt treatment inhibited transcription of a J3-interacting protein kinase gene, PePKS5 (Salt Overly Sensitive 2-Like Protein Kinase 5). To clarify the mechanism by which PeJ3 conferred salinity tolerance, we isolated PeJ3 from P. euphratica and transformed it into Arabidopsis. PeJ3 overexpression inhibited AtPKS5 expression, but had no effect on AtJ3 transcripts. After 10-day exposures to 100 mM NaCl, PeJ3 -transgenic lines showed prolonged survival (40–54.4%) and longer roots (43.8–51.1%) compared to wild-type (WT) and vector control (VC) plants. The observed differences in salt acclimation between transgenic and WT depended on their ability to exclude Na + and maintain intracellular K + . PeJ3 -transgenic Arabidopsis accumulated less Na + in root cells, due at least in part, to the high Na + efflux in roots. K + flux recordings revealed that PeJ3 -transgenic lines lost less K + than WT and VC under salt stress. In vitro and in vivo activity assays revealed that PeJ3 -overexpression upregulated plasma membrane H + -ATPase activity and enhanced H 2 O 2 signaling in salt-stressed Arabidopsis. Consequently, PeJ3 -transgenic plants retained high H + -pumping activity under NaCl salinity, which contributed to K + /Na + homeostasis in roots. In conclusion, PeJ3 overexpression resulted in H + -ATPase activation through transcriptional AtPKS5 suppression and/or interactions with AtPKS5 kinase. Under salinity stress, upregulated H + -pumps (i) promoted Na + /H + exchange across the Arabidopsis plasma membrane, (ii) reduced K + efflux mediated by depolarization-activated plasma membrane channels, and (iii) stimulated H 2 O 2 signaling, which increased cytosolic free Ca 2+ and stimulated Na + extrusion through Salt Overly Sensitive signaling in Arabidopsis.