Metabolome profiling and transcriptome analysis filling the early crucial missing steps of piperine biosynthesis in Piper nigrum L.

Black pepper (Piper nigrum L.), the world renown as the King of Spices, is not only a flavorsome spice but also a traditional herb. Piperine, a species-specific piper amide, is responsible for the major bioactivity and pungent flavor of black pepper. However, several key steps for the biosynthesis of piperoyl-CoA (acyl-donor) and piperidine (acyl-acceptor), two direct precursors for piperine, remain unknown. In this study, we used guilt-by-association analysis of the combined metabolome and transcriptome, to identify two feruloyldiketide-CoA synthases responsible for the production of the C5 side chain scaffold feruloyldiketide-CoA intermediate, which is considered the first and important step to branch metabolic fluxes from phenylpropanoid pathway to piperine biosynthesis. In addition, we also identified the first two key enzymes for piperidine biosynthesis derived from lysine in P. nigrum, namely a lysine decarboxylase and a copper amine oxidase. These enzymes catalyze the production of cadaverine and 1-piperideine, the precursors of piperidine. In vivo and in vitro experiments verified the catalytic capability of them. In conclusion, our findings revealed enigmatic key steps of piperine biosynthetic pathway and thus provide a powerful reference for dissecting the biosynthetic logic of other piper amides.