Identification and analysis of the xyloglucan endotransferase/hydrolase (XTH) family genes in apple

Abstract

Fruit firmness directly determines the commercial value of apples (Malus × domestica Borkh.). The change in its variation is influenced by cell structure and cell wall hydrolases. The significant cell wall hydrolytic enzyme, xyloglucan endotransglycosylase/hydrolase (XTH), is essential for the process of ripening and softening of fruit. In this study, we identified 33 MdXTHs and named them MdXTH1–33 according to their position on the chromosome of apples. Phylogenetic analysis clustered MdXTHs into six groups (A-F), and those with similar gene structure were observed in the same group. Multiple sequence alignment results showed that all MdXTHs have the glycoside hydrolase family 16 domain (Glyco_hydro_16) and the xyloglucan endotransglycosylase C-terminus (XET_C), two highly conserved domains. The promoter of the MdXTHs contained multiple cis-acting elements associated with hormone response. Quantitative real-time PCR analysis suggested that MdXTH3, MdXTH25, and MdXTH26 were most probably involved in fruit softening. The expression of the three MdXTHs was changed and the firmness of fruit was decreased with hormone treaments. In summary, this study provides an extensive analysis of MdXTHs in apples and offers a reference for apple fruit texture breeding through the study of cell wall-related basis.