Identification of a group of XTHs genes responding to heavy metal mercury, salinity and drought stresses in Medicago truncatula.

Xyloglucan endotransglucosylase/hydrolases (XTH) are one of the key enzymes regulating cell wall construction, extension and metabolism. In the study, 44 XTH protein genes from Medicago truncatula genome were identified using bioinformatics, microarray and RT-PCR. Each XTH was showed to possess a highly conserved domain ((D/N)-E-(I/L/F/V)-D-(F/I/L)-E-(F/L)-L-G), and most of XTHs possess four Cys in the C terminal region, which suggests the potential for generating disulfide bonds. Based on the XTH protein sequences, these XTHscan be classified into three major families and each family can be subdivided into more groups. Examination of the genomic location of XTH genes on M. truncatula chromosomes showed that the evolutional expansion of the genes was possibly attributed to localized gene duplications. To investigate the possible involvement of the XTHs responding to heavy metals and other abiotic stresses, the XTH genes were exposed to heavy metal (Hg or Cu), salt and drought stresses. There were 28, 21 and 21 MtXTH genes found to respond to HgCl2, salt and drought stresses, respectively, but their expression were different under the stresses. Some of the XTH genes were well confirmed by quantitative RT-PCR (qRT-PCR). We further specified expression of a XTH gene Medtr4g128580 (MtXTH3) under different environmental stresses, and showed that MtXTH3 was induced by Hg exposure. These results indicated that a group of MtXTHs could be differentially expressed under the environmental stresses.