Xyloglucan endotransglucosylase/hydrolase family genes are required for the plant graft union formation through callus proliferation

Plant grafting, a series of tissue reunion processes, exhibits varying levels of compatibility across different species. Despite extensive research, the response of the scion to various compatible rootstocks remains poorly understood. In this study, we utilized transcriptomic analyses and gene functional validation experiments to investigate the role of xyloglucan endotransglucosylase/hydrolase (XTH) genes and their products in graft healing, specifically examining their effects on callus proliferation and graft survival in response to rootstocks with differing compatibilities across multiple species. Our results indicated that the less compatible bottle gourd rootstocks stimulate increased callus proliferation at the graft junctions with melon (Cucumis melo) scions. Virus-induced gene silencing of a highly expressed XTH gene, CmXTH9, in melon led to lower survival rates and reduced callus proliferation at the graft boundary. Furthermore, grafting accompanied upregulation of 25% to 55% of XTH family genes in the grafts of Arabidopsis thaliana, Nicotiana benthamiana, and Oryza sativa, which are distributed across different phylogenetic branches. Successful heterografts typically induced more family genes with greater upregulation than unsuccessful grafts. Consistently, an Arabidopsis thaliana Atxth4;Atxth7 mutant decreased grafting success rates and diminished callus proliferation at the wound site. These results underscore the conserved function of XTHs in graft union development and highlight their role in graft healing.