Abstract
Xyloglucan endotransglycosylases/hydrolases (XTHs) are a class of enzymes involved in the construction and remodeling of cellulose/xyloglucan crosslinks and play an important role in regulating cell wall extensibility. However, little is known about this class of enzymes in soybean. Here, 61 soybean XTH genes (GmXTHs) were identified and classified into three subgroups through comparative phylogenetic analysis. Genome duplication greatly contributed to the expansion of GmXTH genes in soybean. A conserved amino acid motif responsible for the catalytic activity was identified in all GmXTHs. Further expression analysis revealed that most GmXTHs exhibited a distinct organ-specific expression pattern, and the expression level of many GmXTH genes was significantly associated with ethylene and flooding stress. To illustrate a possible role of XTH genes in regulating stress responses, the Arabidopsis AtXTH31 gene was overexpressed in soybean. The generated transgenic plants exhibited improved tolerance to flooding stress, with a higher germination rate and longer roots/hypocotyls during the seedling stage and vegetative growth stages. In summary, our combined bioinformatics and gene expression pattern analyses suggest that GmXTH genes play a role in regulating soybean stress responses. The enhanced soybean flooding tolerance resulting from the expression of an Arabidopsis XTH also supports the role of XTH genes in regulating plant flooding stress responses.
Highlights
Xyloglucan endotransglycosylases/hydrolases (XET/XTHs named XTHs) are classified as glycoside hydrolase family 16 and play an important role in organ elongation by modifying xyloglucan chains or catalyzing the hydrolysis of xyloglucan [1,2,3,4]
According to the NJ phylogenetic tree, 46 GmXTH genes were clustered in group I/II, and 15 members were classified in group III (Figure 1)
Phylogenetic analysis revealed that the soybean GmXTH gene family was expanded widely in contrast to Arabidopsis and rice, which may correspond to the larger genome of soybean
Summary
Xyloglucan endotransglycosylases/hydrolases (XET/XTHs named XTHs) are classified as glycoside hydrolase family 16 (available online: http://www.cazy.org/fam/GH16.html) and play an important role in organ elongation by modifying xyloglucan chains or catalyzing the hydrolysis of xyloglucan [1,2,3,4]. Several studies have emphasized the significant role of this gene family in the regulation of cell wall extensibility. Overexpression of the BcXTH1 gene from Brassica campestris enhanced stem elongation in Arabidopsis by promoting cell expansion and elongation [5]. Overexpression of GhXTH1 in cotton loosens and elongates cell wall fibers due to cleavage down the xyloglucan-cellulose chains [7,8]. PtxtXET16-34 is strongly expressed in primary-walled xylem. Transgenic hybrid Aspen analysis indicated that wood cell expansion and xyloglucan content were affected when the PtxtXET16-34 gene was overexpressed [9]. AtXTH31 regulates cell wall xyloglucan content, and AtXTH21 influences the development of primary roots by regulating the deposition of cellulose and the thickness of the cell wall in Arabidopsis [10,11]
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