Genome-wide identification and expression analysis of xyloglucan endotransglucosylase/hydrolase genes family in Salicaceae during grafting.

BACKGROUND: Poplar (Populus cathayana)and willow (Salix rehderiana) are important fast-growing trees in China. Grafting plays an important role in improving plant stress resistance and construction of ornamental plants. It is found that willow scions grafted onto poplar rootstocks can form ornamental plants. However, this grafted combination has a low survival rate. Many studies have reported that the xyloglucan endotransglucosylase/hydrolase (XTH) family plays an important role in the healing process of grafts. RESULTS: A total of 38 PtrXTHs and 32 SpuXTHs were identified in poplar and willow respectively, and were classified into three subfamilies. Tandem duplication was the main reason for the expansion of the PtrXTHs. Grafting treatment and Quantitative real time PCR (RT-qPCR) analysis revealed that five XTH genes differentially expressed between self-grafted and reciprocal grafted combinations. Specifically, the high expression levels of SrXTH16, SrXTH17, SrXTH25, PcXTH22 and PcXTH17 may contribute to the high survival rate of the grafted combination with willow scion and poplar rootstock. Subcellular localization identified that the SrXTH16, SrXTH17, SrXTH25, PcXTH17 and PcXTH22 proteins were located on the cell walls. Transcription factors (NAC, MYB and DOF) may regulate the five XTH genes. CONCLUSIONS: This study provides a new understanding of the roles of PcXTH and SrXTH genes and their roles in grafting. Our results will give some hints to explore the molecular mechanisms of PcXTH and SrXTH genes involved in grafting in the future.