Constitutive Overexpression of Myo-inositol-1-Phosphate Synthase Gene (GsMIPS2) from Glycine soja Confers Enhanced Salt Tolerance at Various Growth Stages in Arabidopsis

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The enzyme myo-inositol-1-phosphate synthase (MIPS EC 5.5.1.4) catalyzes the first step of myo-inositol biosynthesis, a product that plays crucial roles in plants as an osmoprotectant, transduction molecule, cell wall constituent and production of stress related molecule. Previous reports highlighted an important role of MIPS family genes in abiotic stresses particularly under salt stress tolerance in several plant species; however, little is known about the cellular and physiological functions of MIPS2 genes under abiotic conditions. In this study, a novel salt stress responsive gene designated GsMIPS2 from wild soybean Glycine soja 07256 was functionally characterized contained an open reading frame (ORF) of 1 533 bp coding a peptide sequence of 510 amino acids along with mass of 56 445 ku. Multiple sequence alignment analysis revealed its 92%-99% similarity with other MIPS family members in legume proteins. Quantitative real-time PCR results demonstrated that GsMIPS2 was induced by salt stress and expressed in roots of soybean. The positive function of GsMIPS2 under salt response at different growth stages of transgenic Arabidopsis was also elucidated. The results showed that GsMIPS2 transgenic lines displayed increased tolerance as compared to WT and atmips2 mutant lines under salt stress. Furthermore, the expression levels of some salt stress responsive marker genes, including KIN1, RD29A, RD29B, P5Cs and COR47 were significantly up-regulated in GsMIPS2 overexpression lines than wild type and atmips2 mutant. Collectively, these results suggested that GsMIPS2 gene was a positive regulator of plant tolerance to salt stress. This was the first report to demonstrate that overexpression of GsMIPS2 gene from wild soybean improved salt tolerance in transgenic Arabidopsis.