BackgroundAgarwood, is a resinous portion derived from Aquilaria sinensis, has been widely used in traditional medicine and incense. 2-(2-phenylethyl)chromones are principal components responsible for the quality of agarwood. However, the molecular basis of 2-(2-phenylethyl)chromones biosynthesis and regulation remains almost unknown. Our research indicated that salt stress induced production of several of 2-(2-phenylethyl)chromones in A. sinensis calli. Transcriptome analysis of A. sinensis calli treated with NaCl is required to further facilitate the multiple signal pathways in response to salt stress and to understand the mechanism of 2-(2-phenylethyl)chromones biosynthesis.ResultsForty one 2-(2-phenylethyl)chromones were identified from NaCl-treated A. sinensis calli. 93 041 unigenes with an average length of 1562 nt were generated from the control and salt-treated calli by Illmunina sequencing after assembly, and the unigenes were annotated by comparing with the public databases including NR, Swiss-Prot, KEGG, COG, and GO database. In total, 18 069 differentially expressed transcripts were identified by the transcriptome comparisons on the control calli and calli induced by 24 h or 120 h salinity stress. Numerous genes involved in signal transduction pathways including the genes responsible for hormone signal transduction, receptor-like kinases, MAPK cascades, Ca2+ signal transduction, and transcription factors showed clear differences between the control calli and NaCl-treated calli. Furthermore, our data suggested that the genes annotated as chalcone synthases and O-methyltransferases may contribute to the biosynthesis of 2-(2-phenylethyl)chromones.ConclusionsSalinity stress could induce the production of 41 2-(2-phenylethyl)chromones in A. sinensis calli. We conducted the first deep-sequencing transcriptome profiling of A. sinensis under salt stress and observed a large number of differentially expressed genes in response to salinity stress. Moreover, salt stress induced dynamic changes in transcript abundance for novel classes of responsive genes involved in signal transduction, including the genes responsible for hormone signal transduction, receptor-like kinases, MAPK cascades, Ca2+ signal transduction, and transcription factors. This study will aid in selecting the target genes to genetically regulate A. sinensis salt-stress signal transduction and elucidating the biosynthesis of 2-(2-phenylethyl)chromones under salinity stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0803-7) contains supplementary material, which is available to authorized users.
Rhamnosides usually possess better bioavailabilities and improved solubilities compared with their aglycons and are a major source of bioactive natural products.
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.
The new curcumin synthase and the unnatural fusion protein reported here are useful for metabolic engineering of pharmaceutically important curcuminoids.
Five 2-(2-phenylethyl)chromones including a new one, (5S,6R,7S,8R)-5, 8-dichloro-6,7 -dihydroxy-2-phenylethyl-5,6,7,8-tetrahydro-4H-chromen-4-one (1), and four known ones (2-5), were isolated from 150 mM NaCl-elicited Aquilaria sinensis cell suspension cultures. In addition, three feruloyl amides (6-8), six nucleosides (9-14), (+)-syringaresinol (15), indole-3-carboxaldehyde (16), and two glycosides (17-18) were also obtained. The structures were unambiguously identified by analysis of their UV, IR, NMR, and HRESIMS data. The absolute configuration of the new 2-(2-phenylethyl)chromone (1) was established by a dimolybdenum tetraacetate-induced circular dichroism experiment. Compared to un-elicited cell lines, the appearance of 2-(2-phenylethyl)chromones in NaCl-treated cells occurred on the 3rd and 5th days of their treatment. 2-(2-Phenylethyl)chromones, feruloyl amides, nucleosides, and lignins have been reported to be closely related to plant defense; therefore, the identification of these compounds from NaCl-elicited A. sinensis cell suspension cultures would be useful for further exploring the mechanism of agarwood formation.
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