Abstract
Caffeic acid O-methyltransferase (COMT), as a multifunctional enzyme involved in various physiological and biochemical processes in lignin metabolism, plays an important role in a plant's response to stress. In this study, we isolated COMT family members from the walnut genome by bioinformatics and analyzed their physicochemical properties and their expression under drought stress to provide gene resources for drought resistance in walnut. The results showed that 33 COMT genes were identified from walnuts and distributed on different chromosomes. The molecular weight of proteins varies greatly. According to the phylogenetic tree, the family can be divided into seven subgroups, which are relatively conservative in evolution and closely related to Arabidopsis thaliana. Promoter analysis showed that the promoter of the walnut COMT gene contains rich cis-elements of plant hormone response and stress response, and the real-time fluorescence scale name can be significantly induced by drought stress. Compared with wild-type Arabidopsis, overexpression JrCOMT19 significantly increased the enzyme activity (SOD, POD, and CAT) and proline content. Meanwhile, overexpression of JrCOMT19 significantly increased the lignin content and expression of related genes. Therefore, JrCOMT plays an important role in responding to drought in walnuts, and overexpression JrCOMT19 can improve the resistance to drought stress by increasing lignin content, antioxidant enzyme activity, and osmotic substance content.