Abstract
Simple SummaryPhenylpropanoids are specialized metabolites playing crucial roles in plant developmental processes and in plant defense towards pathogens. The attachment of sugar moieties to these small hydrophobic molecules renders them more hydrophilic and increases their solubility. The UDP-glycosyltransferase 72 family (UGT72) of plants has been shown to glycosylate mainly two classes of phenylpropanoids, (i) the monolignols that are the building blocks of lignin, the second most abundant polymer after cellulose, and (ii) the flavonoids, which play determinant roles in plant interactions with other organisms and in response to stress. The purpose of this review is to bring an overview of the current knowledge of the UGT72 family and to highlight its role in the homeostasis of these molecules. Potential applications in pharmacology and in wood, paper pulp, and bioethanol production are given within the perspectives.Plants have developed the capacity to produce a diversified range of specialized metabolites. The glycosylation of those metabolites potentially decreases their toxicity while increasing their stability and their solubility, modifying their transport and their storage. The UGT, forming the largest glycosyltransferase superfamily in plants, combine enzymes that glycosylate mainly hormones and phenylpropanoids by using UDP-sugar as a sugar donor. Particularly, members of the UGT72 family have been shown to glycosylate the monolignols and the flavonoids, thereby being involved in their homeostasis. First, we explore primitive UGTs in algae and liverworts that are related to the angiosperm UGT72 family and their role in flavonoid homeostasis. Second, we describe the role of several UGT72s glycosylating monolignols, some of which have been associated with lignification. In addition, the role of other UGT72 members that glycosylate flavonoids and are involved in the development and/or stress response is depicted. Finally, the importance to explore the subcellular localization of UGTs to study their roles in planta is discussed.
Highlights
In order to adapt to terrestrial environments and biotic interactions, plants have developed the capacity to produce a wide range of specialized compounds
This review focuses on two phenylpropanoid families: the monolignolsyalpnrdopthaenofliadvso. nTohiidssre(bvliueewcfiorcclues).eCs oonA,twcooenpzhyemnyelpAr.opanoid families: the monolignols and the flavonoids
A. thaliana plants overexpressing UGT72E2 infected with the fungus V. longisporum showed a 5-fold increase in the coniferin amount, and their susceptibility to the pathogen was reduced [3]
Summary
In order to adapt to terrestrial environments and biotic interactions, plants have developed the capacity to produce a wide range of specialized compounds. Plant UGTs can glycosylate phytohormones such as abscisic acid, auxins, brassinosteroids, and salicylic acid, as well as terpenoids Most of their substrates derive from the phenylpropanoid pathway whose precursors are the aromatic amino acids phenylalanine and tyrosine (Figure 1) [11]. The number of UGTs increased during evolution, consisting of five in Chlamydomonas reinhardtii to more than 200 in trees such as Pinus taeda (gymnosperm) and Populus trichocarpa (angiosperm) This divergence suggests an early and continuous expansion of the UGT family in plants which may be related to their constant adaptation to the terrestrial environment and biotic interactions by producing and regulating specialized metabolites [9,10]. Concerning monolignols and/or their precursors or derivatives, the A. thaliana UGT72E1 and UGT72E2 use coniferaldehyde and sinapaldehyde, and UGT72E2 and UGT72E3 glycosylate ferulic acid, sinapic acid, caffeic acid, coniferyl alcohol, and sinapyl alcohol [58]. Tyrosol Myrtenol 3-oxo-α-ionol Mandelic acid Mandelonitrile Furanmethanethiol Sotolone
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