Flavan-3-ol Galloylation-Related Functional Gene Cluster and the Functional Diversification of SCPL Paralogs in Camellia sp

The high accumulation of galloylated
flavan-3-ols in Camellia sp. is a noteworthy
phenomenon. We identified
a flavan-3-ol galloylation-related functional gene cluster in tannin-rich
plant Camellia sp., which included UGT84A22 and SCPL-AT gene clusters. We
investigated the possible correlation between the accumulation of
metabolites and the expression of SCPL-ATs and UGT84A22. The results revealed that C. sinensis, C. ptilophylla, and C. oleifera accumulated galloylated cis-flavan-3-ols (EGCG), galloylated trans-flavan-3-ols
(GCG), and hydrolyzed tannins, respectively; however, C. nitidissima did not accumulate any galloylated
compounds. C. nitidissima exhibited
no expression of SCPL-AT or UGT84A22, whereas the other three species of Camellia exhibited various expression patterns. This indicated that the functions
of the paralogs of SCPL-AT vary. Enzymatic analysis
revealed that SCPL5 was neofunctionalized as a noncatalytic
chaperone paralog, a type of chaerone-like protein, associating with
flavan-3-ol galloylation; moreover, CsSCPL4 was subfunctionalized
in association with the galloylation of cis- and trans-flavan-3-ols. In C. nitidissima, an SCPL4 homolog was noted with mutations in two
cysteine residues forming a disulfide bond, which suggested that this
homolog was defunctionalized. The findings of this study improve our
understanding of the functional diversification of SCPL paralogs in Camellia sp.

茶树属（Camellia sp.）中儿茶素没食子酸酯的富集是一种值得关注的生物现象。本研究在富含单宁的茶树属植物中，鉴定出一个与儿茶素没食子酸酯化相关的功能基因簇，包括UGT84A22和SCPL-AT基因簇。我们探讨了代谢物积累与SCPL-ATs和UGT84A22表达之间的可能相关性。研究结果表明，茶树（C. sinensis）、毛叶茶（C. ptilophylla）和油茶（C. oleifera）分别积累了儿茶素没食子酸酯（EGCG）、儿茶素没食子酸酯转式儿茶素（GCG）和可水解单宁；然而，光叶茶（C. nitidissima）并未积累任何儿茶素没食子酸酯。光叶茶未表达SCPL-AT或UGT84A22，而其他三种茶树则表现出不同的表达模式。这表明SCPL同源基因的功能存在多样性。酶学分析揭示了SCPL5作为非催化性伴侣同源基因，一种类似于热蛋白的蛋白质，与儿茶素没食子酸酯化相关联；此外，CsSCPL4在连接顺式和反式儿茶素没食子酸酯的儿茶素没食子酸酯化过程中亚功能化。在光叶茶中，发现了一个SCPL4同源基因，其两个半胱氨酸残基发生突变，形成二硫键，这表明该同源基因已失活。本研究成果加深了我们对于茶树属中SCPL同源基因功能多样性的理解。