A Novel CsYABBY3-CsAS1 Feedback Loop Coordinates Trichome Differentiation and Cannabinoid Biosynthesis in Cannabis sativa L.

Glandular trichome development typically coincides with specialized-metabolite production, yet the regulatory mechanisms that synchronizes these processes remain elusive. We uncover a trichome-enriched CsYABBY3-CsAS1 transcriptional module that links glandular trichome differentiation with cannabinoid biosynthesis in cannabis. CsYABBY3, a FILAMENTOUS FLOWER (FIL)/YAB3-family transcription factor, promotes glandular trichome formation and elevates total cannabinoid levels. It directly binds a conserved TAATTAA motif in the promoters of CsPT4 and CsCBDAS, activating their transcription. The R2R3-MYB CsAS1 can also stimulate cannabinoid pathway gene expression independently, but its activity is enhanced in partnership with CsYABBY3. The two factors physically associate and reciprocally upregulate each other, forming a positive feedback loop that amplifies target-gene output. A single residue (M199) in CsYABBY3 is required for CsAS1 interaction and cooperative promoter activation. Comparative evidence suggests broadly conserved FIL/YAB3-AS1 coupling across species, alongside lineage-specific differences in the molecular basis of complex formation. These findings define an engineerable regulatory circuit that connects trichome fate with specialized metabolism and provide a practical route to improve cannabinoid yield.