Huang Keyi, Li Ming, Liu Yajun, Zhu Mengqing, Zhao Guifu, Zhou Yihui, Zhang Lingjie, Wu Yingling, Dai Xinlong, Xia Tao, Gao Liping
School of Life Science, Anhui Agricultural University, Hefei, China.
State Key Laboratory of Tea Plant Biology and Utilization, Anhui Agricultural University, Hefei, China.
Front Plant Sci. 2019 Oct 11;10:1268. doi: 10.3389/fpls.2019.01268. eCollection 2019.
Polyphenols play an important role in the astringent taste of tea [ (L.)] infusions; catechins in phenolic compounds are beneficial to health. The biosynthesis of gallic acid (GA), a precursor for polyphenol synthesis, in tea plants remains unknown. It is well known that 3-dehydroquinate dehydratase/shikimate dehydrogenase (DQD/SDH) is a key enzyme for catalyzing the conversion of 3-dehydroshikimate (3-DHS) to shikimate (SA); it also potentially participates in GA synthesis in a branch of the SA pathway. In this study, four DQD/SDH proteins were produced in . Three DQD/SDHs had 3-DHS reduction and SA oxidation functions. Notably, three DQD/SDHs showed individual differences between the catalytic efficiency of 3-DHS reduction and SA oxidation; DQD/SDHa had higher catalytic efficiency for 3-DHS reduction than for SA oxidation, DQD/SDHd showed the opposite tendency, and DQD/SDHc had almost equal catalytic efficiency for 3-DHS reduction and SA oxidation. , GA was mainly generated from 3-DHS through nonenzymatic conversion. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis showed that and expression was correlated with GA and 1--galloyl-β-D-glucose accumulation in . These results revealed the DQD/SDHc and DQD/SDHd genes are involved in GA synthesis. Finally, site-directed mutagenesis exhibited the mutation of residues Ser-338 and NRT to Gly and DI/LD in the SDH unit is the reason for the low activity of DQD/SDHb for 3-DHS reduction and SA oxidation.
多酚类物质在茶叶浸出液的涩味中起重要作用；酚类化合物中的儿茶素对健康有益。茶树中多酚合成前体没食子酸（GA）的生物合成尚不清楚。众所周知，3-脱氢奎尼酸脱水酶/莽草酸脱氢酶（DQD/SDH）是催化3-脱氢莽草酸（3-DHS）转化为莽草酸（SA）的关键酶；它也可能参与SA途径分支中的GA合成。在本研究中，在[具体生物]中产生了四种DQD/SDH蛋白。三种DQD/SDH具有3-DHS还原和SA氧化功能。值得注意的是，三种DQD/SDH在3-DHS还原和SA氧化的催化效率上表现出个体差异；DQD/SDHa对3-DHS还原的催化效率高于对SA氧化的催化效率，DQD/SDHd表现出相反的趋势，而DQD/SDHc对3-DHS还原和SA氧化的催化效率几乎相等。此外，GA主要通过非酶促转化从3-DHS生成。定量逆转录聚合酶链反应（qRT-PCR）分析表明，[具体基因]的表达与[具体植物]中GA和1-O-没食子酰基-β-D-葡萄糖的积累相关。这些结果表明DQD/SDHc和DQD/SDHd基因参与GA合成。最后，定点诱变表明，SDH单元中Ser-338和NRT残基突变为Gly和DI/LD是DQD/SDHb对3-DHS还原和SA氧化活性低的原因。
