Overexpression of β-1,4-Glucanase Gene EuEG1 Improves Micrografting of Eucommia ulmoides

Adventitious root formation poses a major constraint on the tissue culture and genetic transformation of Eucommia ulmoides. Micrografting offers a new method for the transplantation of genetic transformation, and its success depends on the formation of graft unions. This study used transgenic rootless test-tube seedlings as scions and seedlings from seed as rootstocks during micrografting to avoid the rooting issues that occur during tissue culture and to investigate the role of the EuEG1 gene in the graft healing process. We found that the EuEG1 gene is a vital regulator of graft, and its overexpression contributes to the survival of Eucommia ulmoides micrografting. The EuEG1 gene transgenic plants (TP) used as scions for micrografting presented a significantly higher survival rate than the wild type (WT) and empty vector (EV) regenerated scions. During the grafting healing process, the expression of the EuEG1 gene was higher during the period of callus proliferation, suggesting that the EuEG1 gene was involved in the graft healing process. Histological observation revealed that more calluses tissue appeared at the junction of transgenic scions, and the connection with the rootstock was stronger, which benefits wound healing. These results provide new insights into Eucommia ulmoides micrografting and indicate that the EuEG1 gene can promote wound healing and improve the micrografting survival rate.