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 (GTalpha, GTbeta, and GTgamma) of plant GT factors and each subfamily has a unique composition of predicted motifs. We characterized the OsGTgamma-1 gene, a typical member of the GTgamma subfamily in rice. This gene encodes a protein containing a conserved trihelix domain, and the OsGTgamma-1:GFP fusion protein was targeted to nuclei of rice cells. The transcript level of OsGTgamma-1 was strongly induced by salt stress and slightly induced by drought and cold stresses and abscisic acid treatment. Two other members of the GTgamma subfamily, OsGTgamma-2 and OsGTgamma-3, were also induced by most of the abiotic stresses. These results suggested that the genes of the GTgamma subfamily in rice may be involved in stress responses. A homozygous mutant osgtgamma-1 (with T-DNA inserted in the promoter region of OsGTgamma-1) showed more sensitive to salt stress than wild-type rice. Overexpression of OsGTgamma-1 in rice enhanced salt tolerance at the seedling stage. This evidence suggests that the OsGTgamma subfamily may participate in the regulation of stress tolerance in rice.