Comparative Transcriptome Profiling of Glycine soja Roots Under Salinity and Alkalinity Stresses Using RNA-seq

Saline-alkaline stress can dramatically inhibit plant growth and limit crop production. Wild soybean （Glycine soja） is a crop that adapts well to such environmental stresses. In this study, RNA-sequencing technology was used to analyze the transcriptome profles of G. soja roots subjected to 50 mmol·L^-1 NaHCO3 and 150 mmol·L^-1 NaCl treatments. Totally, 2 125 differentially-expressed genes （DEGs） after NaCl treatment and 1 839 DEGs after NaHCO3 treatment were identifed. The top 14 DEGs revealed by RNA-seq were analyzed using qRT-PCR （quantitative real-time polymerase chain reaction）. Gene ontology （GO） annotation showed that most of DEGs under salt and alkali stresses were enriched in ＂metabolic process＂, ＂catalytic activity＂ and ＂binding＂ terms. To search for transcription factors （TFs） among DEGs, the data were screened against TF database PlantTFDB, and it was found that fve TF families, Apetala2/ethylene-responsive element binding proteins （AP2-EREBP）, V-myb avian myeloblastosis viral oncogene homolog （MYB）, WRKYGQK and Zinc fnger motif （WRKY）, NAM, ATAF1/2, CUC1/2 （NAC） and Cys2/His2 （C2H2） were involved in salt stress response. Other fve TF families, NAC, WRKY, MYB, AP2-EREBP and bZIP were involved in response to alkali stress. These two stress treatments shared NAC, WRKY, AP2-EREBP and MYB, and the only two different TFs were bZIP and C2H2. Forty-eight MYB TFs were differentially expressed under salt and alkali stresses, and most of them were up-regulated. This study provided useful information for further investigation of DEGs and TFs in response to saline and alkaline stresses and helped in understanding the molecular basis of the response of G. soja to saline and alkaline stresses.

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

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 Gs MIPS2 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 Gs MIPS2 was induced by salt stress and expressed in roots of soybean. The positive function of Gs MIPS2 under salt response at different growth stages of transgenic Arabidopsis was also elucidated. The results showed that Gs MIPS2 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, RD29 A, RD29 B, P5 Cs and COR47 were significantly up-regulated in Gs MIPS2 overexpression lines than wild type and atmips2 mutant. Collectively, these results suggested that Gs MIPS2 gene was a positive regulator of plant tolerance to salt stress. This was the first report to demonstrate that overexpression of Gs MIPS2 gene from wild soybean improved salt tolerance in transgenic Arabidopsis.