Saxe Houston J, Horibe Takanori, Balan Bipin, Butterfield Timothy S, Feinberg Noah G, Zabaneh Christopher M, Jacobson Aaron E, Dandekar Abhaya M
Department of Plant Sciences, University of California, Davis, Davis, CA, United States.
College of Bioscience and Biotechnology, Chubu University, Kasugai, Japan.
Front Plant Sci. 2021 Feb 24;12:626483. doi: 10.3389/fpls.2021.626483. eCollection 2021.
We showed previously that gallic acid is produced in walnut from 3-dehydroshikimate by a shikimate dehydrogenase (JrSkDH). This study focuses on the next step in the hydrolysable tannin pathway, the formation of 1--galloyl-β-D-glucose from the phenolic gallic acid and UDP glucose by a glycosyltransferase. JrGGT1 (UGT84A73) and JrGGT2 (UGT84A74) are predicted to be two such glycosyltransferases, which we expressed in tobacco plants. GC-MS analysis of the transgenic tobacco revealed moderate, yet significant alterations in plant secondary metabolism, such as depleted phenolic acids, including gallic acid. We postulate that these effects are due to JrGGT1 and JrGGT2 activity, as JrGGT orthologs glycosylate these phenolic compounds . Moreover, expression in tobacco caused upregulation of shikimic acid pathway metabolites and differing responses in phenylpropanoids, such as phenolic acids and flavonoids. In transcriptome analysis of walnut pellicle tissues, both s showed substantial and significant expression correlations with the gallic acid-producing s and were highly coexpressed with the genetic circuits constituting the shikimic acid and phenylpropanoid biosynthetic pathways. Verification of gene expression by transcriptome analysis of 20 walnut tissues revealed striking similarities with that of the pellicle data, with the greatest expression in roots, wood, buds, and leaves of cv. Chandler: tissues that typically accumulate hydrolysable tannins. Like the transgenic tobacco, pellicle metabolomic analyses revealed that many phenylpropanoids correlated negatively with expression, while shikimic acid pathway metabolites correlated positively with expression. This research supports the hypothesis that JrGGT1 and JrGGT2 play non-trivial roles in metabolism of phenolic acids, flavonoids, and ostensibly, tannins.
我们之前表明，核桃中的没食子酸是由莽草酸脱氢酶（JrSkDH）从3 - 脱氢莽草酸生成的。本研究聚焦于可水解单宁途径的下一步，即由酚类没食子酸和UDP葡萄糖通过糖基转移酶形成1 - 没食子酰基 - β - D - 葡萄糖。JrGGT1（UGT84A73）和JrGGT2（UGT84A74）被预测为两种这样的糖基转移酶，我们在烟草植株中对其进行了表达。对转基因烟草的气相色谱 - 质谱分析显示，植物次生代谢有适度但显著的变化，例如包括没食子酸在内的酚酸减少。我们推测这些效应是由于JrGGT1和JrGGT2的活性，因为JrGGT直系同源物会使这些酚类化合物糖基化。此外，在烟草中的表达导致莽草酸途径代谢物上调，并且在苯丙烷类化合物（如酚酸和类黄酮）中产生不同的反应。在核桃种皮组织的转录组分析中，两者都与产生没食子酸的基因显示出大量且显著的表达相关性，并且与构成莽草酸和苯丙烷生物合成途径的基因回路高度共表达。通过对20种核桃组织的转录组分析对基因表达进行验证，结果显示与种皮数据有惊人的相似性，在钱德勒品种的根、木质部、芽和叶中表达量最高：这些组织通常积累可水解单宁。与转基因烟草一样，种皮代谢组分析表明，许多苯丙烷类化合物与基因表达呈负相关，而莽草酸途径代谢物与基因表达呈正相关。本研究支持以下假设：JrGGT1和JrGGT2在酚酸、类黄酮以及表面上的单宁代谢中发挥重要作用。
