Identification of a diarylpentanoid-producing polyketide synthase revealing an unusual biosynthetic pathway of 2-(2-phenylethyl)chromones in agarwood

Abstract

Abstract2-(2-Phenylethyl)chromones (PECs) are the principal constituents contributing to the distinctive fragrance of agarwood. How PECs are biosynthesized is currently unknown. In this work, we describe a diarylpentanoid-producing polyketide synthase (PECPS) identified from Aquilaria sinensis. Through biotransformation experiments using fluorine-labeled substrate, transient expression of PECPS in Nicotiana benthamiana, and knockdown of PECPS expression in A. sinensis calli, we demonstrate that the C6–C5–C6 scaffold of diarylpentanoid is the common precursor of PECs, and PECPS plays a crucial role in PECs biosynthesis. Crystal structure (1.98 Å) analyses and site-directed mutagenesis reveal that, due to its small active site cavity (247 Å3), PECPS employs a one-pot formation mechanism including a “diketide-CoA intermediate-released” step for the formation of the C6–C5–C6 scaffold. The identification of PECPS, the pivotal enzyme of PECs biosynthesis, provides insight into not only the feasibility of overproduction of pharmaceutically important PECs using metabolic engineering approaches, but also further exploration of how agarwood is formed.

Genome-wide investigation of Cytochrome P450 superfamily of Aquilaria agallocha: association with terpenoids and phenylpropanoids biosynthesis

“…The sweet and lasting scent of agarwood is believed to be because of 2-(2-phenylethyl)chromones (PECs), but mechanism for their biosynthesis is still not clear, except for characterization of few polyketide synthases in A. sinensis which biosynthesizes the precursors of PECs (Wang et al 2022, Wang et al 2017). Interestingly, the core structures of the PECs detected in Aquilaria (Liao et al 2018) suggest that it derives from the common phenylpropanoid pathway (Borejsza-Wysocki et al 1994) through polyketide synthases (type III PKS) (Wang et al 2016) and subsequent hydroxylation and O -methylation producing highly oxygenated chromones (Wang et al 2022, Liao et al 2018). Therefore, we assume that the oxidation and subsequent modifications into different types of chromones (Li et al 2021) are probably catalyses through monooxygenase activity of Aquilaria CYPs.…”

“…It is believed that the unique fragrance that agarwood exhibits is because of these metabolites (Tan et al 2019). Detection of such unique chemical profile indicates CYPs action of hydroxylation and oxidation of sesquiterpenes (Chappell et al 2010) and precursors of phenylethyl chromones (Wang et al 2022) during agarwood formation in Aquilaria plant species.…”

Comprehensive Comparisons between Grafted Kynam Agarwood and Normal Agarwood on Traits, Composition, and In Vitro Activation of AMPK

“…The recent discovery by Tu Pengfei’s group revealed part of the biosynthetic pathway of PECs that differs from flavonoids, and a new diarylpentane-producing polyketide synthase (PECPS) from agarwood was considered to be the key enzyme in the synthesis of 2-(2-phenethyl) chromone [ 50 ]. PECPS was found to use a one-pot formation mechanism to form C6-C5-C6 scaffolds, the precursor of PEC, as shown in Figure 6 a.…”

How Closely Does Induced Agarwood’s Biological Activity Resemble That of Wild Agarwood?

“…Subsequently, the defense mechanisms of the A. sinensis tree were engaged in a response to stop further fungal attack, with linked genes controlling the production of a number of endogenous hydrolases by vesicles, resulting in programmed cell death and cell wall lysis [ 15 , 16 ]. At the same time, a series of precursors for terpenoid backbone biosynthesis and terpene synthase were induced to promote terpenoid synthesis, and the phenol propane metabolic pathway was also activated, such as polyketide synthase, to synthesize diarylpentanoid, which is a prerequisite for the synthesis of the chromones that were subsequently modified by a series of enzymes to generate the various types of 2-(2-phenylethyl)chromones [ 17 , 18 ], as sesquiterpenes and chromones are products of plant resistance to adversity and are also a source of pharmacological action. In comparison to the study by Liao et al, on agarwood caused by the physical trauma method, the total relative content of chromones and sesquiterpenes in induced agarwood produced by fungal inducers was superior [ 19 ].…”