Molecular cloning and characterization of plasma membrane- and vacuolar-type Na⁺/H⁺ antiporters of an alkaline-salt-tolerant monocot, Puccinellia tenuiflora.

A better understanding of salt tolerance in plants might lead to the genetic engineering of crops that can grow in saline soils. Here we cloned and characterized plasma membrane and vacuolar Na⁺/H⁺ antiporters of a monocotyledonous alkaline-tolerant halophyte, Puccinellia tenuiflora. The predicted amino acid sequence of the transporters were very similar to those of orthologs in monocotyledonous crops. Expression analysis showed that (1) NHA was more strongly induced by NaCl in the roots of P. tenuiflora while in rice it was rather induced in the shoots, suggesting that the role of NHA in salt excretion from the roots partly accounts for the difference in the tolerance of the two species, and that (2) NHXs were specifically induced by NaHCO₃ but not by NaCl in the roots of both species, suggesting that vacuolar-type Na⁺/H⁺ antiporters play roles in pH regulation under alkaline salt conditions. Overexpression of the antiporters resulted in increased tolerance of shoots to NaCl and roots to NaHCO₃. Overexpression lines exhibited a lower Na⁺ content and a higher K⁺ content in shoots under NaCl treatments, leading to a higher Na⁺/H⁺ ratio.