A stress-inducible plasma membrane protein 3 (AcPMP3) in a monocotyledonous halophyte, Aneurolepidium chinense, regulates cellular Na+ and K+ accumulation under salt stress

Regulation of ion homeostasis is fundamental to physiological activities in plants. Here, we report on the functional characterization of AcPMP3 [Aneurol-epidium chinense (a monocotyledonous halophyte) plasma membrane protein 3] under salt stress. Expression of AcPMP3-1 and AcPMP3-2 genes was highly induced by various abiotic stresses, such as salt, cold and drought. Furthermore, abscisic acid, H2O2 and salicylic acid also triggered expression of AcPMP3 genes. In the Deltanhal Deltapmr2 Deltapmp3 yeast mutant, which lacks the major Na+ efflux systems (Na+/H+ antiporter and Na+-ATPase), its salt-sensitive phenotype was restored by expressing the AcPMP3-1 gene, and the transformants accumulated lesser amounts of Na+ and K+ than mutant cells under 50 mM NaCl and 500 mM KCl conditions, respectively. These results suggested that AcPMP3-1 plays a role as a regulator of both Na+ and K+ accumulation in the cells. In situ hybridization showed that the AcPMP3-1 transcript was localized in cells of the root cap and root epidermis, which strongly suggested that AcPMP3-1 is essential for regulating Na+/K+ transportation between plant roots and the outer environment under salt stress.