Type IV (pure CBG plants) can happen, theoretically, in a number of ways. In practice, we have evidence of 3 specific routes. (1) double deletion of the THCAS and CBDAS synthases. This is the case in the monoecscious fiber variety “Santhica 27”. (2) Abnormal “nonfunctional” CBDAS synthase in the presence of a normal nonfunctional THCAS synthase. (3) Abnormal “nonfunctional” THCAS synthase in the presence of a normal nonfunctional CBDA synthase.
Other theoretical methods would include the introduction of exogenous forces to shutdown protein expression (i.e. gene silencing via virus or viroid).
I put “nonfunctional” in quotes up there because all of the genes we have found that lead to CBG accumulation have a tendency to maintain catalytic activity for creating other compounds when the precursors are available…which is super super interesting. Synthases (THCA, CBDA, and CBCA) are promiscuous and all retain the ability to create many different chemical products depending on what precursors they are fed. See attached paper from 2018. Elucidation of structure-function relationship of THCA and CBDA synthase from Cannabis sativa L.pdf (1.1 MB)