Molecular characterization of a novel Na+/H+ antiporter cDNA from Eucalyptus globulus

ABSTRACT: Environmental stress factors such as salt, drought and heat are known to affect plant productivity. However, high salinity is spreading throughout the world, currently affecting more than 45 million ha. One of the mechanisms that allow plants to withstand salt stress consists on vacuolar sequestration of Na+, through a Na+/H+ antiporter. We isolated a new vacuolar Na+/H+ antiporter from Eucalyptus globulus from

a cDNA library. The cDNA had a 1626 bp open reading frame encoding a predicted protein of 542 amino acids with a deduced molecular weight of 59.1 KDa. Phylogenetic and bioinformatic analyses indicated that EgNHX1 localized in the vacuole. To assess its role in Na+ exchange, we performed complementation studies using the Na+ sensitive yeast mutant strain Dnhx1. The results showed that EgNHX1 partially

restored the salt sensitive phenotype of the yeast Dnhx1 strain. However, its overexpression in transgenic Arabidopsis confers tolerance in the presence of increasing NaCl concentrations while the wild type plants

exhibited growth retardation. Expression profiles of Eucalyptus seedlings subjected to salt, drought, heat and ABA treatment were established. The results revealed that Egnhx1 was induced significantly only by drought. Together, these results suggest that the product of Egnhx1 from E. globulus is a functional vacuolar Na+/H+ antiporter.