Genome-wide characterization of the xyloglucan endotransglucosylase/hydrolase gene family in Solanum lycopersicum L. and gene expression analysis in response to arbuscular mycorrhizal symbiosis

Xyloglucan endotransglucosylase/hydrolases (XTHs) are a glycoside hydrolase protein family involved in the biosynthesis of xyloglucans, with essential roles in the regulation of plant cell wall extensibility. By taking advantage of the whole genome sequence in Solanum lycopersicum, 37 SlXTHs were identified in the present work. SlXTHs were classified into four subfamilies (ancestral, I/II, III-A, III-B) when aligned to XTHs of other plant species. Gene structure and conserved motifs showed similar compositions in each subfamily. Segmental duplication was the primary mechanism accounting for the expansion of SlXTH genes. In silico expression analysis showed that SlXTH genes exhibited differential expression in several tissues. GO analysis and 3D protein structure indicated that all 37 SlXTHs participate in cell wall biogenesis and xyloglucan metabolism. Promoter analysis revealed that some SlXTHs have MeJA- and stress-responsive elements. qRT-PCR expression analysis of nine SlXTHs in leaves and roots of mycorrhizal colonized vs. non-colonized plants showed that eight of these genes were differentially expressed in leaves and four in roots, suggesting that SlXTHs might play roles in plant defense induced by arbuscular mycorrhiza. Our results provide valuable insight into the function of XTHs in S. lycopersicum, in addition to the response of plants to mycorrhizal colonization.