Characterization and functions of Caffeic acid O-methyltransferase genes in Cucumis sativus against Corynespora cassiicola infection

Lignin is a crucial structural component of plant cell walls and serves as an essential weapon in plant defense responses. Caffeic acid O-methyltransferase (COMT) is a key enzyme in the lignin biosynthetic pathway and also plays a pivotal role in plant disease resistance. However, the sequence and structural characteristics and defense functions of COMT family members in Cucumis sativus have not been extensively studied. In this study, six CsCOMT family genes were identified in C. sativus. Molecular phylogeny and sequence analyses revealed functional similarities and distinct characteristics among the CsCOMT family members. Expression profiles under Corynespora cassiicola infection demonstrated significant upregulation of CsCOMT1, and downregulation of CsCOMT2 and CsCOMT4, indicating their potential involvement in the response to pathogen attack. Functional analyses revealed that CsCOMT1 positively regulated cucumber defense against C. cassiicola, whereas CsCOMT2 and CsCOMT4 negatively regulated this defense, with CsCOMT2 exerting the strongest suppressive effect. Further investigations showed that CsCOMT1 promotes and CsCOMT2 suppresses lignin biosynthesis during plant defense. This study has revealed the unique involvement of different CsCOMT family members in response to C. cassiicola stress and provides strategic targets for breeding disease-resistant cucumber cultivars.