Over-expression of the bacterial nhaA gene in rice enhances salt and drought tolerance

The Escherichia coli nhaA gene encodes a Na+/H+ antiporter, which plays a critical role in ion homeostasis. We transferred a bacterial nhaA gene into rice (Oryza sativa L. ssp. japonica) and detected high expression in the transgenic rice. The germination rate, growth, and average yield per plant of the transgenic lines were better than those of control lines under salt or drought stress. Moreover, the sodium and proline content of the transgenic lines under salt or drought stress was also higher than in control lines, implying that nhaA over-expression enhances osmoregulation by activating the biosynthesis of proline. Tolerance to both salt and drought was compared between transgenic rice over-expressing nhaA and that over-expressing Arabidopsis δ-OAT encoding ornithine-δ-aminotransferase. The transgenic plants with nhaA grew better than those with δ-OAT at high salinity, while the opposite was true for drought stress.