Abstract
Piper gaudichaudianum Kunth (Piperaceae) accumulates gaudichaudianic acid, a prenylated benzopyran, as its major component. Interestingly, this trypanocidal compound occurs as a racemic mixture. Herein, transcriptomic investigations of Piper gaudichaudianum using the RNA-seq approach are reported, and from the analysis of the transcripts expressed it was possible to propose a complete biosynthetic pathway for the production of gaudichaudianic acid, including the steps that originate its precursor, p-hydroxybenzoic acid. Peperomia obtusifolia (L.) A. Dietr. (Piperaceae) also accumulates racemic benzopyrans, however, its chromanes originate from the polyketide pathway, while the chromenes from Piper derives from the shikimate pathway. Recent transcriptomic and proteomic studies of the former species did not identify polyketide synthases involved in the production of the benzopyran moiety, but revealed the expression of tocopherol cyclase, which may be responsible for the cyclization of the 3,4-dihydro-2H-pyran ring. The analysis of the enzymes involved in the secondary metabolism of Piper gaudichaudianum and the comparison with the data previously obtained from Peperomia obtusifolia can provide valuable information on how these compounds are biosynthesized.
Highlights
Chromanes and chromenes, which are secondary metabolites commonly found in some species from Piper and Peperomia genera (Piperaceae), are characterized by the presence of a benzopyran ring with various levels of oxidation.[1,2,3] This nucleus is considered a privileged structure that is very common in bioactive natural products, such as coumarins, flavones, tocopherols (vitamin E) and tetrahydrocannabinoids.[4,5]The benzopyran moieties, 2H-chromenes and chromanes, isolated from Piper gaudichaudianum and Peperomia obtusifolia, respectively, have been demonstrated as potent trypanocidal compounds.[6,7] Curiously, both classes of compounds occur as racemic mixtures in these species, though their formation follows two distinct biosynthetic routes.[6,8,9] In Piper gaudichaudianum, chromenes originate from the shikimate pathway and use p-hydroxybenzoic acid (p-HBA) as a precursor.[10]
Candidate genes involved in benzopyran biosynthesis In Piper gaudichaudianum, chromenes originate from the precursor p-hydroxybenzoic acid (p-HBA) via the shikimate pathway
This study presents for the first time the transcriptome analysis of Piper gaudichaudianum using a ‐generation sequencing approach
Summary
Chromanes and chromenes, which are secondary metabolites commonly found in some species from Piper and Peperomia genera (Piperaceae), are characterized by the presence of a benzopyran ring with various levels of oxidation.[1,2,3] This nucleus is considered a privileged structure that is very common in bioactive natural products, such as coumarins, flavones, tocopherols (vitamin E) and tetrahydrocannabinoids.[4,5]The benzopyran moieties, 2H-chromenes and chromanes, isolated from Piper gaudichaudianum and Peperomia obtusifolia, respectively, have been demonstrated as potent trypanocidal compounds.[6,7] Curiously, both classes of compounds occur as racemic mixtures in these species, though their formation follows two distinct biosynthetic routes.[6,8,9] In Piper gaudichaudianum, chromenes originate from the shikimate pathway and use p-hydroxybenzoic acid (p-HBA) as a precursor.[10]. The annotated transcripts were analyzed by searching them against the KEGG (Kyoto Encyclopedia of Genes and Genomes) database for KEGG (K) number assignments and subsequent reconstruction of the biosynthetic pathways active in Piper gaudichaudianum leaves.
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