Expansin(EXP)plays an important role in plant response to environmental stress by regulating cell wall relaxation.To explore the role of EXP genes in soybean response to abiotic stress,two soybean EXP genes(GmEXPB5 and GmEXPB7)and their protein sequences were analyzed by bioinformatics,and their expression levels were detected by real-time fluorescent quantitative PCR(qRT-PCR).The results were as follows:(1)The GmEXPB5 and GmEXPB7 were located on chromosomes 10 and 12 of soybean,and encoded proteins containing 272 and 267 amino acids,respectively.The molecular weight of GmEXPB5 protein was 29.07 kD and the theoretical isoelectric point was 7.51.The molecular weight of GmEXPB7 protein was 29.09 kD and the theoretical isoelectric point was 8.66.Both GmEXPB5 and GmEXPB7 were stable hydrophilic proteins,and localized in the cell wall.Both GmEXPB5 and GmEXPB7 proteins contained a signal peptide sequence and a conserved DPBB_1 structural domain.(2)GmEXPB5 protein had the closest affinity with CaEXPB15 protein of Cicer arietinum,and GmEXPB7 protein was closely related to EXPB3 proteins of Spatholobus suberectus,Vigna angularis and V.unguiculata.(3)GmEXPB5 and GmEXPB7 were expressed in root,stem and leaf of soybean,and their expression levels in root and leaf were significantly higher than those in stem.(4)GmEXPB5 and GmEXPB7 could respond to salt,drought and cold stresses in soybean seedlings.(5)The promoter region of GmEXPB5 contained two types of stress-related cis-elements(ABRE and ARE).The promoter region of GmEXPB7 contained five types of stress-related cis-elements(ABRE,ARE,CGTCA-motif,TC-rich repeats and MBS).In conclusion,these results indicate that GmEXPB5 and GmEXPB7 can participate in the response of soybean to abiotic stress.
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