Disruption of RCI2A leads to over-accumulation of Na+ and increased salt sensitivity in Arabidopsis thaliana plants

For plant salt tolerance, it is important to regulate the uptake and accumulation of Na+ ions. The yeast pmp3 mutant which lacks PMP3 gene accumulates excess Na+ ions in the cell and shows increased Na+ sensitivity. Although the function of PMP3 is not fully understood, it is proposed that PMP3 contributes to the restriction of Na+ uptake and consequently salt tolerance in yeasts. In this paper, we have investigated whether the lack of RCI2A gene, homologous to PMP3 gene, causes a salt sensitive phenotype in Arabidopsis (Arabidopsis thaliana (L.) Heynh.) plants; and to thereby indicate the physiological role of RCI2A in higher plants. Two T-DNA insertional mutants of RCI2A were identified. Although the growth of rci2a mutants was comparable with that of wild type under normal conditions, high NaCl treatment caused increased accumulation of Na+ and more reduction of the growth of roots and shoots of rci2a mutants than that of wild type. Undifferentiated callus cultures regenerated from rci2a mutants also accumulated more Na+ than that from wild type under high NaCl treatment. Furthermore, when wild-type and rci2a plants were treated with NaCl, NaNO3, Na2SO4, KCl, KNO3, K2SO4 or LiCl, the rci2a mutants showed more reduction of shoot growth than wild type. Under treatments of tetramethylammonium chloride, CaCl2, MgCl2, mannitol or sorbitol, the growth reduction was comparable between wild-type and rci2a plants. These results suggested that RCI2A plays a role directly or indirectly for avoiding over-accumulation of excess Na+ and K+ ions in plants, and contributes to salt tolerance.