Functional characterization of two acyltransferases from Populus trichocarpa capable of synthesizing benzyl benzoate and salicyl benzoate, potential intermediates in salicinoid phenolic glycoside biosynthesis. (May 2015)

• Record Type: Journal Article
• Authors: Chedgy, Russell J.; Köllner, Tobias G.; Constabel, C. Peter
• Is Part Of: Phytochemistry. Volume 113(2015:May)
• Page Start: 149
• Page End: 159
• Publication Date: 2015-05
• Subjects: PtBEBT Populus trichocarpa benzoyl-CoA: benzyl alcohol O-benzoyltransferase -- PtSABT Populus trichocarpa benzoyl-CoA: salicyl alcohol O-benzoyltransferase -- PG phenolic glycoside; Poplar -- Populus trichocarpa -- Salicaceae -- Salicinoid phenolic glycosides -- Herbivore defense -- Benzoyltransferase -- Escherichia coli heterologous expression; Botanical chemistry -- Periodicals; Biochemistry -- Periodicals; Botany -- Periodicals; Chimie végétale -- Périodiques; 572.2
• DOI: 10.1016/j.phytochem.2014.10.018
• Languages: English
• ISSNs: 0031-9422

Abstract

Graphical abstract: Two BAHD-type acyl transferases with hypothetical roles in salicinoid metabolism of poplar were functionally characterized. PtSABT catalyzes the synthesis of salicyl benzoate from benzoyl-CoA and salicyl alcohol, while PtBEBT catalyzes formation of benzyl benzoate from benzoyl-CoA and benzyl alcohol. Highlights: Two Populus trichocarpa BAHD acyl transferases were functionally characterized. PtSABT and PtBEBT catalyze the formation of salicyl benzoate and benzyl benzoate, respectively. These enzymes are hypothesized to participate in salicinoid phenolic glycoside metabolism. Abstract: Salicinoids are phenolic glycosides (PGs) characteristic of the Salicaceae and are known defenses against insect herbivory. Common examples are salicin, salicortin, tremuloidin, and tremulacin, which accumulate to high concentrations in the leaves and bark of willows and poplars. Although their biosynthetic pathway is not known, recent work has suggested that benzyl benzoate may be a potential biosynthetic intermediate. Two candidate genes, named PtACT47 and PtACT49, encoding BAHD-type acyl transferases were identified and are predicted to produce such benzylated secondary metabolites. Herein described are the cDNA cloning, heterologous expression and in vitro functional characterization of these two BAHD acyltransferases. Recombinant PtACT47 exhibited low substrate selectivity and could utilize acetyl-CoA, benzoyl-CoA, and cinnamoyl-CoA as acyl donors with a variety of alcohols as acyl acceptors. This enzyme showed the greatest K m / K cat ratio (45.8 nM −1 s −1 ) and lowest K m values (45.1 μM) with benzoyl-CoA and salicyl alcohol, and was named benzoyl-CoA: salicyl alcohol O -benzoyltransferase (PtSABT). Recombinant PtACT49 utilized a narrower range of substrates, including benzoyl-CoA and acetyl-CoA and a limited number of alcohols. Its highest K m / K cat (31.8 nM −1 s −1 ) and lowest K m (55.3 μM) were observed for benzoyl-CoA and benzyl alcohol, and it was named benzoyl-CoA: benzyl alcohol O -benzoyltransferase (PtBEBT). Both enzymes were also capable of synthesizing plant volatile alcohol esters, such as hexenyl benzoate, at trace levels. Although the activities demonstrated are consistent with roles in salicinoid biosynthesis, direct tests of this hypothesis using transgenic poplar must still be performed.