Gene duplication and divergence affecting drug content in Cannabis sativa

Abstract

SummaryCannabis sativa is an economically important source of durable fibers, nutritious seeds, and psychoactive drugs but few economic plants are so poorly understood genetically.Marijuana and hemp were crossed to evaluate competing models of cannabinoid inheritance and to explain the predominance of tetrahydrocannabinolic acid (THCA) in marijuana compared with cannabidiolic acid (CBDA) in hemp. Individuals in the resulting F 2 population were assessed for differential expression of cannabinoid synthase genes and were used in linkage mapping. Genetic markers associated with divergent cannabinoid phenotypes were identified.Although phenotypic segregation and a major quantitative trait locus (QTL) for the THCA/ CBDA ratio were consistent with a simple model of codominant alleles at a single locus, the diversity of THCA and CBDA synthase sequences observed in the mapping population, the position of enzyme coding loci on the map, and patterns of expression suggest multiple linked loci. Phylogenetic analysis further suggests a history of duplication and divergence affecting drug content.Marijuana is distinguished from hemp by a nonfunctional CBDA synthase that appears to have been positively selected to enhance psychoactivity. An unlinked QTL for cannabinoid quantity may also have played a role in the recent escalation of drug potency.

Characterisation of cannabinoid composition in a diverse Cannabis sativa L. germplasm collection

“…4). GC analysis of chemotype II has typically demonstrated a more narrow range skewed towards a high CBD total to THC total ratio (De Meijer et al 1992;Hillig and Mahlberg 2004;Weiblen et al 2015), although a low CBD total to THC total ratio similar to those reported here have been observed in Southeast Asian landraces (Tipparat et al 2012). Nevertheless, this is the first time that such a wide range in chemotype II variability has been unequivocally assigned to genotype and heterozygosity of THCAS and CBDAS.…”

“…All things being equal chemotype II individuals would be expected to have a CBD total :THC total ratio close to 1:1. Deviation from this ratio within chemotype II has previously been proposed to be due either to increased catalytic efficiency of CBDA synthase over THCA synthase (Weiblen et al 2015), or from genetic vs environment interactions (Potter 2009). Considering that ratios of chemotype II plants deviated both towards CBD total and THC total , and that all plants were grown in environmentally controlled conditions, it could be suggested that chemotype II variability is largely influenced by genetic control.…”

“…The identification of multiple sequence variants of THCAS or CBDAS within individuals (Kojoma et al 2006;Onofri et al 2015;Van Bakel et al 2011;Weiblen et al 2015) and segregation in mapping populations, suggests that at least two closely linked loci govern THC(V)A and CBD(V)A composition. Recent evidence indicates that THCAS and CBDAS are positioned 1.1 cM apart (Weiblen et al 2015).…”

“…The identification of multiple sequence variants of THCAS or CBDAS within individuals (Kojoma et al 2006;Onofri et al 2015;Van Bakel et al 2011;Weiblen et al 2015) and segregation in mapping populations, suggests that at least two closely linked loci govern THC(V)A and CBD(V)A composition. Recent evidence indicates that THCAS and CBDAS are positioned 1.1 cM apart (Weiblen et al 2015). The presence of contrasting functional allelic variants of THCAS and CBDAS occurring at multiple loci may be a possible explanation as to the range and variability in CBD total : THC total ratios occurring within chemotype II, and is also consistent with the reduced representation of chemotype IV within the gene pool.…”

Genomic and Chemical Diversity inCannabis

“…A single locus with co-dominant alleles was proposed to explain patterns of inheritance for THCA to CBDA ratios (de Meijer et al, 2003;Staginnus et al, 2014). However more recent quantitative trait loci (QTL) mapping experiments (Weiblen et al, 2015), expression studies (Onofri et al, 2015), and genomic analyses (van Bakel et al, 2011) paint a more complex scenario with several linked paralogs responsible for the various THCA and CBDA phenotypes. Other cannabinoids such as cannabigerol (CBG) (Borrelli et al, 2014), cannabichromene (CBC) (Izzo et al, 2012), and delta-9-tetrahydrocannabivarin (THCV) (Mcpartland et al, 2015) demonstrate pharmacological promise, and can also be produced at high levels by the plant (de Meijer and Hammond, 2005;de Meijer and Hammond, 2016;de Meijer et al, 2008).…”