Summary
Phenolic compounds are secondary metabolites involved in several plant growth and development processes, including resistance to biotic and abiotic stresses. The biosynthetic pathways leading to the vast diversity of plant phenolic products often include an acylation step, with phenolic compounds being the donor or acceptor molecules. To date, two acyltransferase families using phenolic compounds as acceptor or donor molecules have been described, with each using a different ‘energy-rich’ acyl donor. BAHD-acyltransferases, named after the first four biochemically characterized enzymes of the group, use acyl-CoA thioesters as donor molecules, whereas SCPL (Serine CarboxyPeptidase Like)-acyltransferases use 1-O-β-glucose esters. Here, common and divergent specifications found in the literature for both enzyme families were analyzed to answer the following questions. Are both acyltransferases involved in the synthesis of the same molecule (or same group of molecules)? Are both acyltransferases recruited in the same plant? How does the subcellular localization of these enzymes impact metabolite trafficking in plant cells?

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/nph.13498

BAHD or SCPL acyltransferase? What a dilemma for acylation in the world of plant phenolic compounds.

Summary UDP-glycosyltransferases (GTases, UGT) catalyze the transfer of the sugar moiety from the uridine-diphosphate-activated monosaccharide (e.g. uridine-diphosphate-5’-glucose, UDPG) molecule to the specific acceptor. Glycosides contain aglycons attached by a β-glycosidic bond to C1 of the saccharide moiety. Glycosylation is one of the mechanisms maintaining cellular homeostasis through the regulation of the level, biological activity, and subcellular distribution of the glycosylated compounds. The glycosides play various functions in plant cells, such as high-energy donors, or signalling molecules, and are involved in biosynthesis of cell walls. Plant cells exhibit structural and functional diversity of UGT proteins. The Arabidopsis thaliana genome contains more than 100 genes encoding GTases, which belong to 91 families, and are deposited in the CAZY (Carbohydrate Active enzyme) database (www. cazy.org/GlycosylTransferases.html). The largest UGT1 class is divided into 14 subfamilies (A-N), and includes proteins containing highly conserved 44-amino acid PSPG (Plant Secondary Product Glycosyltransferase) motif at the C-terminus. The PSPG motif is involved in the binding of UDP-sugar donors to the enzyme. UGT1’s catalyze the biosynthesis of both ester-type and ether-type conjugates of plant hormones (phytohormones). Conjugation of the phytohormones is an important mechanism that regulates the concentration of physiological active hormone levels during growth and development of plants. Glycoconjugation of phytohormones is widespread in the plant kingdom and all known phytohormones are able to form these conjugates. Most plant hormone conjugates do not indicate physiological activity, but rather are involved in transport, storage and degradation of the phytohormones. UDPG-dependent glycosyltransferases possess high substrate specificity, even within a given class of phytohormones. In many cases, the phenotype of plants is strongly affected by loss-of-function mutations in UGT genes. In this paper, advances in the isolation and characterization of glycosyltransferases of all plant hormones: auxin, brassinosteroids, cytokinin, gibberellin, abscisic acid, jasmonates, and salicylate is described

/pdf/udp-glycosyltransferases-of-plant-hormones-5ee4qcn7eb.pdf

Udp-Glycosyltransferases of Plant Hormones

Hydroxycinnamoyltransferases are enzymes transferring hydroxycinnamoyl units like cinnamoyl, 4-coumaroyl, caffeoyl, feruloyl and sinapoyl moieties from an activating residue such as coenzyme A or glucose or activated as hydroxycinnamoyl ester (e.g. chlorogenate) to an acceptor molecule, most commonly to an OH or NH2 group as ester or amide. The hydroxycinnamoyl groups play either a “decorating” role or are building blocks of more complex structures. Proteins catalysing hydroxycinnamoyl transfer have been known for many decades and are nowadays investigated on molecular and structural levels. At least four different protein families give rise to enzymes with hydroxycinnamoyltransferase activity: serine carboxypeptidase-like proteins, tyramine hydroxycinnamoyltransferase-like enzymes, BAHD acyltransferases and GDSL-lipase/esterase-like enzymes. Interestingly, the same or very similar products can be formed by enzymes from different enzyme classes and using differently activated hydroxycinnamoyl units. This review will summarise the current literature data on the features of hydroxycinnamoyltransferases from the four different enzyme groups.

Hydroxycinnamoyltransferases in plant metabolism

A serine carboxypeptidase-like acyltransferase catalyzes synthesis of indole-3-acetic (IAA) ester conjugate in rice (Oryza sativa).

Enzymes of acyltransferase families transfer an acyl moiety from energy-rich donor molecules to various acceptors, contributing to the vast diversification of plant secondary metabolites. All plant acyltransferases are divided into two families: BAHD and serine carboxypeptidase-like (SCPL) acyltransferases. Since the characterization of isobutyryltransferase from Lycopersicon pennellii, the first known SCPL acyltransferase, a number of enzymes from this family have been identified in various plants. These enzymes are potential targets for studying the evolution of plant enzymes, as they are believed to be undergoing evolutionary changes. The aim of this work is to summarize our current knowledge of SCPL acyltransferases.

Plant SCPL acyltransferases: multiplicity of enzymes with various functions in secondary metabolism

1-O-(indole-3-acetyl)-β-d-glucose: sugar indoleacetyl transferase (1-O-IAGlc-SugAc) is a novel enzyme catalyzing the transfer of the indoleacetyl (IA) moiety from 1-O-(indole-3-acetyl)-β-d-glucose to several saccharides to form ester-linked IAA conjugates. 1-O-IAGlc-SugAc was purified from liquid endosperm of Zea mays by fractionation with ammonium sulphate, anion-exchange, Blue Sepharose chromatography, affinity chromatography on Concanavalin A-Sepharose, adsorption on hydroxylapatite and preparative PAGE. The obtained enzyme preparation indicates only one band of Rf 0.67 on 8% non-denaturing PAGE consisting of two polypeptides of 42 and 17 kDa in SDS/PAGE. Highly purified 1-O-IAGlc-SugAc shows maximum transferase activity with monosaccharides (mannose, glucose, and galactose), lower activity with disaccharides (melibiose, gentobiose) and trisaccharide (raffinose) and minimal enzymatic activity with oligosaccharides from the raffinose family as well. The novel acyltransferase exhibits, besides its primary indoleacetylation of sugar, minor hydrolytic and disproportionation activities producing free IAA and supposedly 1,2-di-O-(indole-3-acetyl)-β-glucose, respectively. Presumably, 1-O-IAGlc-SugAc, like 1-O-indole-3-acetyl-β-d-glucose-dependent myo-inositol acyltransferase (1-O-IAGlc-InsAc), is another member of the serine carboxypeptidase-like (SCPL) acyltransferase family.

/pdf/novel-1-o-indole-3-acetyl-b-d-glucose-dependent-3k7nx0juq6.pdf

Stanisław Kowalczyk

Papers

Novel 1- O -indole-3-acetyl-β- d -glucose-dependent acyltransferase transferring indoleacetyl moiety to some mono- di- and oligosaccharides