Identification and expression analysis of caffeoyl-coenzyme A O-methyltransferase family genes related to lignin biosynthesis in tea plant (Camellia sinensis).

Tea plant, an economically important crop, is used in producing tea, which is a non-alcoholic beverage. Lignin, the second most abundant component of the cell wall, reduces the tenderness of tea leaves and affects tea quality. Caffeoyl-coenzyme A O-methyltransferase (CCoAOMT) involved in lignin biosynthesis affects the efficiency of lignin synthesis and lignin composition. A total of 10 CsCCoAOMTs were identified based on tea plant genome. Systematic analysis of CCoAOMTs was conducted for its physicochemical properties, phylogenetic relationships, conserved motifs, gene structure, and promoter cis-element prediction. Phylogenetic analysis suggested that all the CsCCoAOMT proteins can be categorized into three clades. The promoters of six CsCCoAOMT genes possessed lignin-specific cis-elements, indicating they are possibly essential for lignin biosynthesis. According to the distinct tempo-spatial expression profiles, five genes were substantially expressed in eight tested tissues. Most CsCCoAOMT genes were expressed in stems and leaves in three tea plant cultivars 'Longjing 43,' 'Anjibaicha,' and 'Fudingdabai' by RT-qPCR detection and analysis. The expression levels of two genes (CsCCoAOMT5 and CsCCoAOMT6) were higher than those of the other genes. The expression levels of most CsCCoAOMT genes in 'Longjing 43' were significantly higher than that those in 'Anjibaicha' and 'Fudingdabai.' Correlation analysis revealed that only the expression levels of CsCCoAOMT6 were positively correlated with lignin content in the leaves and stems. These results lay a foundation for the future exploration of the roles of CsCCoAOMTs in lignin biosynthesis in tea plant.