The role of GmXTH1, a new xyloglucan endotransglycosylase/hydrolase from soybean, in regulating soybean root growth at seedling stage

Soybean is an important crop for both food and oil, providing high quality protein and oil for humans and animals. Drought stress has an significant effect on the yield and quality of soybean. In the early vegetative stage of soybean, the developed root system can effectively improve the tolerance of soybean plant to drought. Xyloglucan endoglycosylase/hydrolase (XTH) is a cell wall remodeling enzyme involved in cell wall expansion and degradation. However, there are few studies on XTHs regulation of root growth and response to drought stress in soybean seedlings.The objectives of this study were to clone GmXTH1 gene and determine the effects of over and interference-expression of GmXTH1 on soybean root development at seedling stage. A 1,015 bp full-length of the GmXTH1 gene was cloned from soybean (Glycine max L. Merril) cv. RM18 with a 840 bp open reading frame (ORF) of a putative protein. The over and interference expression vectors of GmXTH1 were transformed into soybean using Agrobacterium method. Transformed strains OEA1, OEA3, IEA4, IEA5 were identified by molecular detection methods. The roots of transformed strains OEA1and OEA3 with GmXTH1 gene overexpression are clearly developed and the root phenotypic attributes, including main root length, primary root number, lateral root length, root surface area, root volume, root dry weight, root fresh weight are higher than the control. In contrast, root attributes of IEA4 and IEA5 with GmXTH1 gene interference expression were significantly lower than those of the control, suggesting that the expression of GmXTH1 gene has an important effect on the soybean root growth and development at seedling stage. Under drought stress conditions, the activities of Superoxide dismutase (SOD), Peroxidase(POD)and Catalase(CAT)in the transgenic strains with an overexpression of the GmXTH1 gene were significantly increased, and the root activity, leaf relative water content and total chlorophyll content were ranked in order of OEAs, CK, and IEAs. In conclusion, GmXHT1 plays an important role in the growth of soybean root at seedling stage. Overexpression of GmXTH1 gene can promote root development of soybean seedling. The results of activities of protective enzymes (SOD, POD, CAT), root activity, leaf relative water content and total chlorophyll content under drought stress indicated that transgenic strains OEA1 and OEA3 with overexpressing GmXTH1 gene were resistant to drought stress, suggesting that GmXTH1 may play a positive role in responding to drought stress at soybean seedling stage.