Deactivating mutations in the catalytic site of a companion serine carboxypeptidase-like acyltransferase enhance catechin galloylation in <i>Camellia</i> plants

Galloylated flavan-3-ols are key quality and health-related compounds in tea plants of <i>Camellia</i> section <i>Thea</i>. <i>Camellia ptilophylla</i> and <i>Camellia sinensis</i> are two representative species known for their high levels of galloylated flavan-3-ols. Building on our knowledge of galloyl catechin biosynthesis in <i>C. sinensis</i>, we now focus on the biosynthesis of galloylated phenolics in <i>C. ptilophylla</i>, aiming to elucidate the mechanisms underlying the high accumulation of these compounds in <i>Camellia</i> species. The phenolic compounds in <i>C. ptilophylla</i> were identified and quantified using chromatographic and colorimetric methods. Genes involved in polyphenol galloylation were identified by correlating gene expression with the accumulation of galloylated phenolics across 18 additional <i>Camellia</i> species and one related species using Weighted Gene Coexpression Network Analysis. Key findings include the coexpression of SCPL4/2 and SCPL5 subgroup enzymes as crucial for galloylation of catechins, while SCPL3 and SCPL8 showed enzymatic activity related to hydrolyzable tannin synthesis. Variations in the amino acid sequences of SCPL5, particularly in the catalytic triad (T-D-Y vs S-D-H) observed in <i>C. ptilophylla</i> and <i>C. sinensis</i>, were found to significantly affect enzymatic activity and epigallocatechin gallate (EGCG) production. In conclusion, this research provides important insights into the metabolic pathways of <i>C. ptilophylla</i>, emphasizing the critical role of SCPL enzymes in shaping the phenolic profile within the section <i>Thea</i>. The findings have significant implications for the cultivation and breeding of tea plants with optimized phenolic characteristics.