文摘
Na+/H+ antiporters (NHX) are ubiquitous transmembrane proteins that play a key role in salt tolerance of plants. In this study, the sequence of 3 Arabidopsis NHX genes (AtNHX2-) were compared with other AtNHX members. Putative cis-elements analysis identified elements that have been associated with stress responses. The activities of the promoters AtNHX2- were studied in transgenic plants carrying corresponding promoter-β-glucuronidase (GUS) fusions. The AtNHX2 promoter-GUS analysis indicated that AtNHX2 was expressed in constitutive pattern with high GUS activity in roots and leaves. AtNHX2 promoter activity was not up-regulated by NaCl or abscisic acid (ABA), in contrast the AtNHX1 promoter which was previously studied. The AtNHX3 and AtNHX4 promoters showed tissue-specific activities. Strong GUS activity was detected in roots and vascular bundles of the stele in plants carrying an AtNHX4 promoter-GUS fusion, and GUS activity increased under salt stress suggesting a function related to salt tolerance. Transgenic plants carrying the AtNHX3 promoter-GUS fusion showed strong GUS activity in petals, stamens and tops of siliques, suggesting a possible role of AtNHX3 in flower and seed development. Results of histochemical analysis suggested that AtNHX2- are involved in divergent functions and are differentially regulated under abiotic stress. The structure of AtNHX4 was predicted to include 12 transmembrane regions and a NHX domain. Overexpression of AtNHX4 in Arabidopsis transgenic lines confers greater salt tolerance than in wild type plants. These results suggest that AtNHX4 may encode a putative vacuolar NHX that plays an important role in salt tolerance.