The glucosyltransferase UGT72E2 is responsible for monolignol 4‐O‐glucoside production in Arabidopsis thaliana

Abstract

SummaryThe phenylpropanoid pathway in plants leads to the synthesis of a wide range of soluble secondary metabolites, many of which accumulate as glycosides. In Arabidopsis, a small cluster of three closely related genes, UGT72E1-E3, encode glycosyltransferases shown to glucosylate several phenylpropanoids in vitro, including monolignols, hydroxycinnamic acids and hydroxycinnamic aldehydes. The role of these genes in planta has now been investigated through genetically downregulating the expression of individual genes or silencing the entire cluster. Analysis of these transgenic Arabidopsis plants showed that the levels of coniferyl and sinapyl alcohol 4-O-glucosides that accumulate in light-grown roots were significantly reduced. A 50% reduction in both glucosides was observed in plants in which UGT72E2 was downregulated, whereas silencing the three genes led to a 90% reduction, suggesting some redundancy of function within the cluster. The gene encoding UGT72E2 was constitutively overexpressed in transgenic Arabidopsis to determine whether increased glucosylation of monolignols could influence flux through the soluble phenylpropanoid pathway. Elevated expression of UGT72E2 led to increased accumulation of monolignol glucosides in root tissues and also the appearance of these glucosides in leaves. In particular, coniferyl alcohol 4-O-glucoside accumulated to massive amounts (10 lmol g )1 FW) in root tissues of these plants. Increased glucosylation of other phenylpropanoids also occurred in plants overexpressing this glycosyltransferase. Significantly changing the pattern of glycosides in the leaves also led to a pronounced change in accumulation of the hydroxycinnamic ester sinapoyl malate. The data demonstrate the plasticity of phenylpropanoid metabolism and the important role that glucosylation of secondary metabolites can play in cellular homeostasis.

Glycosyltransferases from Oat (Avena) Implicated in the Acylation of Avenacins

“…This may be important when considering the function of these enzymes in vivo because UGTs with overlapping substrate specificity that are co-expressed in the same cell types may show functional redundancy. For example, in A. thaliana UGT72E2 has been shown to glycosylate monolignol in the phenylpropanoid pathway, yet a ugt72E2 T-DNA insertion line shows only a 50% reduction in monolignol glucoside due to functional redundancy (36). Two other related GTs (UGT72E1 and UGT72E3) are also able to glucosylate monolignol.…”

Recombinant expression and functional characterisation of regiospecific flavonoid glucosyltransferases from Hieracium pilosella L.

“…Besides the arbutin synthase from R. serpentina (Hefner et al 2002) mentioned above, subfamily 72 contains A. thaliana glucosyltransferases, including UGT72B1, which possesses both N-and O-glucosyltransferase activity. This enzyme was assigned to the detoxiWcation of xenobiotics (Loutre et al 2003;Brazier-Hicks and Edwards 2005;Brazier-Hicks et al 2007), whereas the UGTs 72E1-E3 are involved in the glucosylation of monolignols, hydroxycinnamic acids, and hydroxycinnamic aldehydes Lanot et al 2006). H. pilosella UGT90A7 belongs to group C and, to the best of our knowledge, an enzyme of this subfamily has never been characterised.…”

Manipulation of plant metabolic pathways by transcription factors

“…However, at the same time, the amount of the end product or its precursors on the branching pathway may decrease by a shortage of a precursor at the branching point ( Figure 1B, metabolite d). Such reductions are often observed when an enzyme gene is ectopically expressed (Okinaka et al 2003;Lanot et al 2006Lanot et al , 2008. In case of transcriptional repressors, adverse effects would be expected to occur in a metabolic pathway when the transcriptional repressor is ectopically expressed.…”