From dawn ‘til dusk: daytime progression regulates primary and secondary metabolism in Cannabis glandular trichomes

<em>Cannabis sativa </em>L. glandular trichomes (GTs) synthesise large amounts of specialised secondary metabolites, predominantly cannabinoids and terpenoids. The associated demand for carbon and energy makes GTs strong sink tissues and there is indication that their secondary metabolism is coupled to the availability of photoassimilates. Many metabolites, including secondary metabolites, show diurnal patterns of flux but it is unknown whether cannabinoids and terpenoids are regulated by time of day. We quantified cannabinoids, terpenoids and the GT proteome over a 12-hour light period in flowers of Hindu Kush, a high-tetrahydrocannabinol (THC) cultivar. Major cannabinoids showed significant changes over the course of day, resulting in an increase in total measured cannabinoids. Major terpenoids also showed changes, with sesquiterpenes generally decreasing with day progression. While monoterpenes generally did not decrease, the second most abundant, a-pinene, increased. The GT proteome changed the most within the first six hours of the day and analysis of differentially abundant proteins indicated upregulation of primary metabolism. Surprisingly, key cannabinoid biosynthetic enzymes decreased with daytime progression despite increases in cannabinoid content, which might indicate that daytime increases of photoassimilates are the main driver of cannabinoid regulation. This first reporting of variability of cannabinoid and terpenoid biosynthesis over the course of the day has implications for Cannabis research and production.