Genetic regulation of trichome development and importance for breeding in C. sativa
Glandular trichomes are the site of cannabinoid biosynthesis in Cannabis sativa. While trichomes are located on all above-ground surfaces of the plant, glandular trichomes are most highly concentrated on the flowers of the inflorescence; particularly the unfertilized female inflorescence. Glandular trichomes form when an epidermal pavement cell receives non-cell autonomous signals from surrounding tissue to develop into a sessile capitate glandular trichome. The developing trichome receives additional signals during floral development which causes it to become a bulbous trichome, which then develops into a capitate stalked trichome (CSG).
The CSG has a multicellular stalk connected to a basal cell, which has a rosette of stipe cells and secretory cells above it. Genes encoding cannabinoid biosynthetic enzymes are expressed in these secretory cells leading to the production of THC and CBD, two commercially important cannabinoids, as well as monoterpenes which use some metabolites that also feed into the cannabinoid biosynthetic pathway. Only when the trichome reaches the capitate stalked phase does it begin to produce considerable amounts of cannabinoids.
We are identifying heretofore uncharacterized cannabis genes that control glandular trichome initiation and development as one approach to maximize cannabinoid production in cannabis. We have identified three cannabis proteins that are similar to transcription factors (TF’s) which are known to be involved in glandular trichome initiation and development in other species: TF-X, Y and Z. We are characterizing their function and association with the increasing level of cannabinoids in the maturing flowers. We have found that the expression of these genes is correlated with floral maturation as well as the expression of genes in the cannabinoid biosynthesis pathway. Furthermore, we have studied the impact of a variety of hormones on these transcription factors, and the resulting impact on cannabinoid production. We have found that TF-Y is upregulated by gibberellic acid, a hormone which is instrumental to the induction of flowering in cannabis. Additionally, we have transformed TF-Y into Nicotiana tabacum, a model plant used for the study of trichome development and have observed an impact on trichome phenotype. We are also working on the transient transformation of trichome gland cells in order to study the impact of TF’s on the cannabinoid biosynthesis pathway.