Systematic analysis of GT factor family of rice reveals a novel subfamily involved in stress responses

GT factors constitute a plant-specific transcription factor family with a conserved trihelix DNA-binding domain. In this study, comprehensive sequence analysis suggested that 26 putative GT factors exist in rice. Phylogenetic analysis revealed three distinctive subfamilies (GT alpha, GT beta, and GT gamma) of plant GT factors and each subfamily has a unique composition of predicted motifs. We characterized the OsGT gamma-1 gene, a typical member of the GT gamma subfamily in rice. This gene encodes a protein containing a conserved trihelix domain, and the OsGT gamma-1:GFP fusion protein was targeted to nuclei of rice cells. The transcript level of OsGT gamma-1 was strongly induced by salt stress and slightly induced by drought and cold stresses and abscisic acid treatment. Two other members of the GT gamma subfamily, OsGT gamma-2 and OsGT gamma-3, were also induced by most of the abiotic stresses. These results suggested that the genes of the GT gamma subfamily in rice may be involved in stress responses. A homozygous mutant osgt gamma-1 (with T-DNA inserted in the promoter region of OsGT gamma-1) showed more sensitive to salt stress than wild-type rice. Overexpression of OsGT gamma-1 in rice enhanced salt tolerance at the seedling stage. This evidence suggests that the OsGT gamma subfamily may participate in the regulation of stress tolerance in rice.