Huang, Keyi Li, Ming Liu, Yajun Zhu, Mengqing Zhao, Guifu Zhou, Yihui Zhang, Lingjie Wu, Yingling Dai, Xinlong Xia, Tao Gao, Liping Image_3_Functional Analysis of 3-Dehydroquinate Dehydratase/Shikimate Dehydrogenases Involved in Shikimate Pathway in Camellia sinensis.jpeg <p>Polyphenols play an important role in the astringent taste of tea [Camellia sinensis (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 CsDQD/SDH proteins were produced in Escherichia coli. Three CsDQD/SDHs had 3-DHS reduction and SA oxidation functions. Notably, three CsDQD/SDHs showed individual differences between the catalytic efficiency of 3-DHS reduction and SA oxidation; CsDQD/SDHa had higher catalytic efficiency for 3-DHS reduction than for SA oxidation, CsDQD/SDHd showed the opposite tendency, and CsDQD/SDHc had almost equal catalytic efficiency for 3-DHS reduction and SA oxidation. In vitro, GA was mainly generated from 3-DHS through nonenzymatic conversion. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis showed that CsDQD/SDHc and CsDQD/SDHd expression was correlated with GA and 1-O-galloyl-β-D-glucose accumulation in C. sinensis. These results revealed the CsDQD/SDHc and CsDQD/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 CsDQD/SDHb for 3-DHS reduction and SA oxidation.</p> Camellia sinensis;3-dehydroquinate dehydratase/shikimate dehydrogenase;gallic acid;shikimate pathway;site-directed mutagenesis 2019-10-11
    https://frontiersin.figshare.com/articles/figure/Image_3_Functional_Analysis_of_3-Dehydroquinate_Dehydratase_Shikimate_Dehydrogenases_Involved_in_Shikimate_Pathway_in_Camellia_sinensis_jpeg/9968657
10.3389/fpls.2019.01268.s004