Molecular and functional analyses of rice NHX-type Na+/H+ antiporter genes

Abstract

We previously cloned a vacuolar Na+/H+ antiporter gene (OsNHX1) from rice (Oryza sativa). Here we identified four additional NHX-type antiporter genes in rice (OsNHX2 through OsNHX5) and performed molecular and functional analyses of those genes. The exon-intron structure of the OsNHX genes and the phylogenetic tree of the OsNHX proteins suggest that the OsNHX proteins are categorized into two subgroups (OsNHX1 through OsNHX4 and OsNHX5). OsNHX1, OsNHX2, OsNHX3, and OsNHX5 can suppress the Na+, Li+, and hygromycin sensitivity of yeast nhx1 mutants and their sensitivity to a high K+ concentration. The expression of OsNHX1, OsNHX2, OsNHX3, and OsNHX5 is regulated differently in rice tissues and is increased by salt stress, hyperosmotic stress, and ABA. When we studied the expression of β-glucuronidase (GUS) driven by either the OsNHX1 or the OsNHX5 promoter, we observed activity in the stele, the emerging part of lateral roots, the vascular bundle, the water pore, and the basal part of seedling shoots with both promoters. In addition, each promoter had a unique expression pattern. OsNHX1 promoter-GUS activity only was localized to the guard cells and trichome, whereas OsNHX5 promoter-GUS activity only was localized to the root tip and pollen grains. Our results suggest that the members of this gene family play important roles in the compartmentalization into vacuoles of the Na+ and K+ that accumulate in the cytoplasm and that the differential regulation of antiporter gene expression in different rice tissues may be an important factor determining salt tolerance in rice.

Two Rice Authentic Histidine Phosphotransfer Proteins, OsAHP1 and OsAHP2, Mediate Cytokinin Signaling and Stress Responses in Rice

“…In Arabidopsis, cytokinin appears to have both positive (Elkeltawi and Croteau, 1987;Gadallah, 1999;Iqbal and Ashraf, 2005;Iqbal et al, 2006) and negative (Tran et al, 2007) effects on salt tolerance, suggesting that the role of cytokinin is complex and that its influence depends on a variety of factors. The salt overly sensitive (SOS) signaling system increases plant salt tolerance by activating Na + -extrusion antiporters (Shi et al, 2002;Martínez-Atienza et al, 2007); the high-affinity K + transporter1;1 (OsHKT1;1), which mediates inward Na + transport (Jabnoune et al, 2009), protects young leaves from ion toxicity by the accumulation of Na + and Cl 2 in old leaves (Wang et al, 2012); and Na + /H + antiporter genes (OsNHXs) play roles in the compartmentalization of Na + into vacuoles (Fukuda et al, 2011). These are all functional genes required to prevent sodium toxicity.…”

Evaluation of Saltol QTL Introgression in Rice: A Study on Co-Existence of Salinity Tolerance and Phytoremediation Effect

“…Molecular and functional analyses of rice NHX-type Na + /H + antiporter genes revealed the important role of this gene in the compartmentalization of Na + into vacuoles (Fukuda et al, 2011). With the advent of Next Generation Sequencing technologies the donor which has the highest expression of Na + /H + antiporter genes can be identified and the same can be utilized to develop salinity tolerant rice genotypes with phytoremediation capacity by molecular breeding.…”

AtCCX1 transports Na+ and K+ in Pitch pastoris

“…However, recently, CCXs in Arabidopsis were also found to be related to Na + compartmentation. Heterologous expression of AtCCX3 in yeast increased accumulation of Na + in yeast (Morris et al, 2008), similar to NHX1 to promote Na + uptake (Kinclova et al, 2003;Darley et al, 2000;Fukuda et al, 2011). When compared with NHX1, AtCCX3 simultaneously transported K + and Mn 2+ apart from Na + .…”