The Chromomethylase CsCMT2 Negatively Affects Catechin Accumulation in Tea Plants

Catechins are the major bioactive polyphenolic compounds in tea (Camellia sinensis) and key determinants of its astringency, flavor quality, and health value. Although DNA methylation has been associated with catechin biosynthesis in tea, the roles of chromomethylase (CMT) genes in regulating catechin accumulation remain unclear. In this study, we characterized the CMT gene family in C. sinensis and identified four members: CsCMT1, CsCMT2, CsCMT3a, and CsCMT3b. All CsCMT genes were preferentially expressed in buds and young leaves, the tissues harvested for tea production, and CsCMT2 showed the most pronounced cultivar-dependent expression under Colletotrichum gloeosporioides infection. Transient overexpression of CsCMT2 in tea leaves decreased the contents of all six measured catechins (EGCG, GCG, EGC, GC, EC, and C), with EGCG showing the greatest reduction. It also downregulated seven catechin biosynthetic genes, namely CsPAL, CsC4H, CsCHI, CsF3'5'H, CsDFR, CsANR, and CsSCPL1A. Conversely, virus-induced gene silencing of CsCMT2 increased total catechin content and upregulated these genes. Caffeine content was not significantly affected by either manipulation, indicating a relatively specific effect on catechin metabolism. These results suggest that CsCMT2 negatively affects catechin accumulation associated with transcriptional changes in pathway genes and is a potential target for modulating catechin composition and flavor quality in tea germplasm improvement.