Two UGT84A Family Glycosyltransferases Regulate Phenol, Flavonoid, and Tannin Metabolism in Juglans regia (English Walnut)

Abstract

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-O-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 in vitro. Moreover, JrGGT 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 JrGGTs showed substantial and significant expression correlations with the gallic acid-producing JrSkDHs and were highly coexpressed with the genetic circuits constituting the shikimic acid and phenylpropanoid biosynthetic pathways. Verification of JrGGT 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 Juglans regia cv. Chandler: tissues that typically accumulate hydrolysable tannins. Like the transgenic tobacco, pellicle metabolomic analyses revealed that many phenylpropanoids correlated negatively with JrGGT expression, while shikimic acid pathway metabolites correlated positively with JrGGT expression. This research supports the hypothesis that JrGGT1 and JrGGT2 play non-trivial roles in metabolism of phenolic acids, flavonoids, and ostensibly, tannins.

Transcriptomic and Metabolic Analysis of Fruit Development and Identification of Genes Involved in Raffinose and Hydrolysable Tannin Biosynthesis in Walnuts

“…33 Two UDP-glycosyltransferases, JrGGT1 and JrGGT2, were predicted to play roles in the metabolism of phenolic acids, flavonoids, and tannins by a combination of multiple-omics data analysis and experimental assays. 34 According to these studies, we could conclude that it is possible to dissect the complex biosynthesis pathway of the nutrient compositions in walnut kernels by combining a highquality genome sequence and newly developed multiple-omics technology, including RNA sequencing (RNA-Seq) and metabolic assays.…”

“…The phylloquinone pathway genes involved in the formation of a compound other than phylloquinone (1,4-dihydroxynaphthoic acid, DHNA) were investigated using comparative transcriptomics in combination with targeted metabolic profiling in various black walnut organs . Two UDP-glycosyltransferases, JrGGT1 and JrGGT2, were predicted to play roles in the metabolism of phenolic acids, flavonoids, and tannins by a combination of multiple-omics data analysis and experimental assays . According to these studies, we could conclude that it is possible to dissect the complex biosynthesis pathway of the nutrient compositions in walnut kernels by combining a high-quality genome sequence and newly developed multiple-omics technology, including RNA sequencing (RNA-Seq) and metabolic assays.…”

Genome-Wide Analysis and Identification of UDP Glycosyltransferases Responsive to Chinese Wheat Mosaic Virus Resistance in Nicotiana benthamiana

“…The subcellular localization of NbUGT12, NbUGT16, and NbUGT17 remained unchanged during CWMV infection ( Figure 5 ), indicating that they should not affect viral infection through changes in localization. Many UGT genes are involved in the phenylpropanoid metabolism in plants, which can regulate the accumulation of metabolites such as hydroxycinnamic acids, coumarins, flavonoids, phenols, and tannins [ 66 , 67 , 68 , 69 , 70 ]. Flavonoid glycosylation is typically mediated by UGTs [ 1 ].…”

Genome-Wide Identification of Genes Related to Biosynthesis of Phenolic Acid Derivatives in Bletilla striata at Different Suspension Culture Stages

“…The metabolism of phenolic acid compounds was a relatively complicated process. The shikimic acid pathway, the phenylpropanoid metabolic pathway, and the flavonoid metabolic pathway were the main pathways for the synthesis of phenolic acid compounds (Saxe et al, 2021). Among them, phenylalanine and tyrosine are direct precursors of phenolic acid biosynthesis, which are converted from glucose into a multistep metabolism via the shikimic acid pathway and then into the phenylpropanoid metabolic pathway (Feduraev et al, 2020;El-Shora et al, 2021).…”