Comparative analysis of Arabidopsis UGT74 glucosyltransferases reveals a special role of UGT74C1 in glucosinolate biosynthesis

Abstract

SUMMARYThe study of glucosinolates and their regulation has provided a powerful framework for the exploration of fundamental questions about the function, evolution, and ecological significance of plant natural products, but uncertainties about their metabolism remain. Previous work has identified one thiohydroximate S-glucosyltransferase, UGT74B1, with an important role in the core pathway, but also made clear that this enzyme functions redundantly and cannot be the sole UDP-glucose dependent glucosyltransferase (UGT) in glucosinolate synthesis. Here, we present the results of a nearly comprehensive in vitro activity screen of recombinant Arabidopsis Family 1 UGTs, which implicate other members of the UGT74 clade as candidate glucosinolate biosynthetic enzymes. Systematic genetic analysis of this clade indicates that UGT74C1 plays a special role in the synthesis of aliphatic glucosinolates, a conclusion strongly supported by phylogenetic and gene expression analyses. Finally, the ability of UGT74C1 to complement phenotypes and chemotypes of the ugt74b1-2 knockout mutant and to express thiohydroximate UGT activity in planta provides conclusive evidence for UGT74C1 being an accessory enzyme in glucosinolate biosynthesis with a potential function during plant adaptation to environmental challenge.

Transporters in plant sulfur metabolism

“…Following fusion of the activated aldoximes to GSH, the produced S-alkylthiohydroximates are converted to thiohydroximates by the C-S lyase SUR1 (Mikkelsen et al, 2004). The last but one reaction in GSL biosynthesis is the S-glucosylation of thiohydroximates by glucosyltransferases of the UGT74 family, with UGT74C1 recently shown to glucosylate Met-derived substrates (Douglas Grubb et al, 2014). The final step of GSL biosynthesis is a SOTs, which form GSL from desulfoGSL.…”

The bifurcation of the cyanogenic glucoside and glucosinolate biosynthetic pathways

“…The precise nature of this reaction with respect to the involvement of glutathione‐ S ‐transferase and nitrile‐oxide or aci‐ nitro compound intermediates has remained unresolved (Bak et al ., ; Geu‐Flores et al ., ; Hirai et al ., ). The conjugate formed is initially processed by the action of γ‐glutamyl peptidase (Geu‐Flores et al ., , ) and converted into the final glucosinolate structure by a C–S lyase (SUR1) (Boerjan et al ., ), S ‐glucosyl transferase (Grubb et al ., ) and a sulfotransferase (Piotrowski et al ., ).…”

flasher, a novel mutation in a glucosinolate modifying enzyme, conditions changes in plant architecture and hormone homeostasis

“…We previously hypothesized that bp acts to control inflorescence architecture by countermanding the action of a vascular-borne growth inhibitor (Douglas and Riggs, 2005). It is well documented that GSL molecules can move through the vasculature (Brudenell et al, 1999;Chen et al, 2001;Nour-Eldin et al, 2012), and numerous GSL biosynthetic genes are expressed in vascular tissues (Reintanz et al, 2001;Chen et al, 2003;Grubb et al, 2004Grubb et al, , 2014Gigolashvili et al, 2007;Malitsky et al, 2008;Li et al, 2011;Kong et al, 2015). Limited evidence suggests that some GS-OX enzymes are expressed in the vasculature (Li et al, 2011) and, to extend these data, we examined FSH expression by employing both transcriptional (GUS) and translational (GFP) fusions in transgenic lines.…”