Unveiling the role of VcCOMT38 as a specific O-methyltransferase for enhancing lignin biosynthesis: insights from blueberry and cross-species analysis

Lignin is a significant secondary metabolite produced through the phenylpropanoid pathway. As a vital component of the plant cell wall, lignin affects various fruit characteristics, including size, seed quantity, and firmness. In this study, we conducted comprehensive identification and phylogenetic analysis of 265 Caffeic acid O-methyltransferase (COMT) genes across ten different plant species, including Vaccinium corymbosum and four other Vaccinium species. The results reveal that VcCOMT38 is a promising structural gene for the biosynthesis of lignin in blueberry. An in vitro enzymatic assay of VcCOMT38 demonstrated that it is a special enzyme in the lignin biosynthesis pathway and prefers to use caffeic acid as a substrate over 5-hydroxyferulic acid. Transient overexpression and silencing of VcCOMT38 in Vaccinium corymbosum ‘Northland’ fruits demonstrated that VcCOMT38 participates in lignin biosynthesis and contributes to both an increased number of immature seeds and enhanced fruit firmness. The heterologous overexpression of VcCOMT38 in Nicotiana benthamiana revealed that this gene could increase the lignin content and the syringyl/guaiacyl (S/G) ratio, which determines the maximum monomer yield during lignin depolymerization. These results highlight VcCOMT38 as a crucial gene in lignin biosynthesis and its potential for improving lignin production in industry through genetically modified woody plants.