Molecular Character, Phylogeny and Expression of Tomato LeNHX3 Gene Involved in Multiple Adverse Stress Responses

Abstract

Crop production is severely affected by high salt stress. To obtain more salt-tolerant crops by genetic modification, it is crucial to explore some key genes associated with salt tolerance. LeNHX3 gene is considered one putative Na ⁺/H ⁺ antiporter with the ability of improving plant salt tolerance by maintaining intracellular ionic balance in tomato, however, limited information about it has been reported. Here, we report the structure, phylogenetic evolution and expression of LeNHX3 gene from wild type tomato (Lycopersicon esculentum Mill cv. Ailsa Craig). Sequence analysis showed that LeNHX3 encodes a protein containing 10 transmembrane domains, with a typical conserved amiloride binding domain presented in the third transmembrane domain. An interesting discovery also showed that sequence of LeNHX3 was more conserved than its allele protein collected by GenBank (designated as LeNHX3-GB in this study) when compared with others Na+/H+ antiporters. Homology modeling results showed that the structure of LeNHX3 protein consists mainly of α-helix and random coil, it has similar tertiary structure to that of LeNHX3-GB, however, inter-residue interactions were found to be further strengthened in LeNHX3. Phylogenetic analysis showed LeNHX3 was clustered with vacuolar Na ⁺/H ⁺ antiporters and has distant relationship to plasma membrane Na ⁺/H ⁺ antiporters. Expression profiles analysis indicated LeNHX3 gene was constitutively expressed in roots, stems and leaves, its expression was also induced by salt, low temperature and abscisic acid. The results presented in this work provide new insights into LeNHX3 gene, it is particularly important that one new LeNHX3 allele from wild tomato was mined, which can serve as a candidate gene for improving plant stress tolerance by genetic engineering.