The biosynthetic origin of psychoactive kavalactones in kava.

Kava (Piper methysticum) is an ethnomedicinal shrub native to the Polynesian islands with well-established anxiolytic and analgesic properties. Its main psychoactive principles, kavalactones, form a unique class of polyketides that interact with the human central nervous system through mechanisms distinct from those of conventional psychiatric drugs. However, an unknown biosynthetic machinery and difficulty in chemical synthesis hinder the therapeutic use of kavalactones. In addition, kava also produces flavokavains, which are chalconoids with anticancer properties structurally related to kavalactones. Here, we report de novo elucidation of the key enzymes of the kavalactone and flavokavain biosynthetic network. We present the structural basis for the evolutionary development of a pair of paralogous styrylpyrone synthases that establish the kavalactone scaffold and the catalytic mechanism of a regio- and stereo-specific kavalactone reductase that produces a subset of chiral kavalactones. We further demonstrate the feasibility of engineering styrylpyrone production in heterologous hosts, thus opening a way to develop kavalactone-based non-addictive psychiatric therapeutics through synthetic biology.

Complete Pathway Elucidation and Heterologous Reconstitution of Rhodiola Salidroside Biosynthesis.

Salidroside is a bioactive tyrosine-derived phenolic natural product found in medicinal plants under the Rhodiola genus. In addition to their anti-fatigue and anti-anoxia roles in traditional medicine, Rhodiola total extract and salidroside have also displayed medicinal properties as anti-cardiovascular diseases and anti-cancer agents. The resulting surge in global demand of Rhodiola plants and salidroside has driven some species close to extinction. Here, we report the full elucidation of the Rhodiola salidroside biosynthetic pathway utilizing the first comprehensive transcriptomics and metabolomics datasets for Rhodiola rosea. Unlike the previously proposed pathway involving separate decarboxylation and deamination enzymatic steps from tyrosine to the key intermediate 4-hydroxyphenylacetaldehyde (4-HPAA), Rhodiola contains a pyridoxal phosphate-dependent 4-HPAA synthase that directly converts tyrosine to 4-HPAA. We further identified genes encoding the subsequent 4-HPAA reductase and tyrosol:UDP-glucose 8-O-glucosyltransferase, respectively, to complete salidroside biosynthesis in Rhodiola. We show that heterologous production of salidroside can be achieved in the yeast Saccharomyces cerevisiae as well as the plant Nicotiana benthamiana through transgenic expression of Rhodiola salidroside biosynthetic genes. This study provides new tools for engineering sustainable production of salidroside in heterologous hosts.