Plant-based aromatic prenyltransferases for activation of phenolic compounds

Helichrysum umbraculigerum plants produce and accumulate phytocannabinoid pre-cursors in their aerial plant parts. Both olivetolic acid and cannabigerolic acid (CBGA-C5), the last common precursor of the pharmaceutically interesting cannabinoids tetrahydrocannabinol, cannabidiol, and cannabichromene, were detected. Furthermore, the first protocols for micropropagation of H. umbraculigerum plants were successful-ly established, including the induction of callus material, the generation of suspension cultures, and the formation of aerial plant tissues from leaf discs. These protocols serve as a basis for the establishment of genetically modified plants and based on them, approaches for the transformation of H. umbraculigerum plants were tested in the present work.
In addition, two novel gene sequences were identified from H. umbraculigerum that encode enzymes capable of forming CBGA-C5. These were heterologously expressed in yeast and tested for their function in vitro. The enzymes act as prenyl-transferases that prenylate olivetolic acid with geranyl diphosphate. Based on their sequences, protein topologies were predicted, consisting of their transmembrane domains and conserved motifs. These suggest an association to the aromatic homo-gentisate prenyltransferase family.
Besides Cannabis sativa, H. umbraculigerum is the first plant from which enzymes capable of producing CBGA-C5 have been identified so far. Remarkably, the sequence similarities, of the H. umbraculigerum prenyltransferase genes identified in this work and the genes known from C. sativa that encode CBGA-C5-producing en-zymes, are very low, with a maximum of 37% at the DNA level. The encoded amino acid sequences are also decidedly different with nearly 55% sequence identities. The application of these HuPTs for heterologous production of phytocannabinoids in yeast was tested via multicopy integrations into the yeast genome.