Ahmad Muhammad Zulfiqar, Li Penghui, She Guangbiao, Xia Enhua, Benedito Vagner A, Wan Xiao Chun, Zhao Jian
State Key Laboratory of Tea Plant Biology and Utilization, Anhui Agricultural University, Hefei, China.
Division of Plant & Soil Sciences, West Virginia University, Morgantown, WV, United States.
Front Plant Sci. 2020 Jun 25;11:848. doi: 10.3389/fpls.2020.00848. eCollection 2020.
Tea ( L.) leaves synthesize and concentrate a vast array of galloylated catechins (e.g., EGCG and ECG) and non-galloylated catechins (e.g., EGC, catechin, and epicatechin), together constituting 8%-24% of the dry leaf mass. Galloylated catechins account for a major portion of soluble catechins in tea leaves (up to 75%) and make a major contribution to the astringency and bitter taste of the green tea, and their pharmacological activity for human health. However, the catechin galloylation mechanism in tea plants is largely unknown at molecular levels. Previous studies indicated that glucosyltransferases and serine carboxypeptidase-like acyltransferases (SCPL) might be involved in the process. However, details about the roles of SCPLs in the biosynthesis of galloylated catechins remain to be elucidated. Here, we performed the genome-wide identification of SCPL genes in the tea plant genome. Several SCPLs were grouped into clade IA, which encompasses previously characterized SCPL-IA enzymes with an acylation function. Twenty-eight tea genes in this clade were differentially expressed in young leaves and vegetative buds. We characterized three SCPL-IA enzymes (CsSCPL11-IA, CsSCPL13-IA, CsSCPL14-IA) with galloylation activity toward epicatechins using recombinant enzymes. Not only the expression levels of these SCPLIA genes coincide with the accumulation of galloylated catechins in tea plants, but their recombinant enzymes also displayed β-glucogallin:catechin galloyl acyltransferase activity. These findings provide the first insights into the identities of genes encoding glucogallin:catechin galloyl acyltransferases with an active role in the biosynthesis of galloylated catechins in tea plants.
茶树（L.）叶片合成并积累了大量的没食子酰化儿茶素（如表没食子儿茶素没食子酸酯和儿茶素没食子酸酯）和非没食子酰化儿茶素（如表儿茶素、儿茶素和表儿茶素），它们共同占干叶质量的8%-24%。没食子酰化儿茶素占茶叶中可溶性儿茶素的大部分（高达75%），对绿茶的涩味和苦味以及对人体健康的药理活性有重要贡献。然而，茶树中儿茶素没食子酰化机制在分子水平上很大程度上尚不清楚。先前的研究表明，葡萄糖基转移酶和丝氨酸羧肽酶样酰基转移酶（SCPL）可能参与该过程。然而，SCPL在没食子酰化儿茶素生物合成中的具体作用细节仍有待阐明。在此，我们在茶树基因组中对SCPL基因进行了全基因组鉴定。几个SCPL被归入IA进化枝，该进化枝包含先前已鉴定的具有酰化功能的SCPL-IA酶。该进化枝中的28个茶树基因在幼叶和营养芽中差异表达。我们使用重组酶对三种具有表儿茶素没食子酰化活性的SCPL-IA酶（CsSCPL11-IA、CsSCPL13-IA、CsSCPL14-IA）进行了表征。这些SCPLIA基因的表达水平不仅与茶树中没食子酰化儿茶素的积累一致，而且它们的重组酶还表现出β-葡萄糖没食子酸：儿茶素没食子酰基转移酶活性。这些发现首次揭示了在茶树没食子酰化儿茶素生物合成中起积极作用的编码葡萄糖没食子酸：儿茶素没食子酰基转移酶的基因身份。
