Molecular and functional analyses of rice NHX-type Na+/H+ antiporter genes.
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.
Division of Plant Sciences, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki, Japan. fukuda@affrc.go.jp
Atsunori
A
Fukuda
Atsuko
A
Nakamura
Naho
N
Hara
Seiichi
S
Toki
Yoshiyuki
Y
Tanaka
D000040:Abscisic Acid / Q000494:pharmacology; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics*; D005816:Genetic Complementation Test; D005966:Glucuronidase / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D009928:Organ Specificity / Q000187:drug effects / Q000235:genetics; D012275:Oryza / Q000166:cytology / Q000187:drug effects / Q000235:genetics*; D010802:Phylogeny; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics; D036226:Seedlings / Q000187:drug effects / Q000235:genetics; D012965:Sodium Chloride / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics* / Q000378:metabolism*; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics
D017923:Sodium-Hydrogen Exchangers; D012965:Sodium Chloride; D000040:Abscisic Acid; D005966:Glucuronidase