Complex Patterns of Cannabinoid Alkyl Side-Chain Inheritance in Cannabis

Abstract

The cannabinoid alkyl side-chain represents an important pharmacophore, where genetic targeting of alkyl homologs has the potential to provide enhanced forms of Cannabis for biopharmaceutical manufacture. Delta(9)-tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA) synthase genes govern dicyclic (CBDA) and tricyclic (THCA) cannabinoid composition. However, the inheritance of alkyl side-chain length has not been resolved, and few studies have investigated the contributions and interactions between cannabinoid synthesis pathway loci. To examine the inheritance of chemical phenotype (chemotype), THCAS and CBDAS genotypes were scored and alkyl cannabinoid segregation analysed in 210 F 2 progeny derived from a cross between two Cannabis chemotypes divergent for alkyl and cyclic cannabinoids. Inheritance patterns of F 2 progeny were non-Gaussian and deviated from Mendelian expectations. However, discrete alkyl cannabinoid segregation patterns consistent with digenic as well as epistatic modes of inheritance were observed among F 2 THCAS and CBDAS genotypes. These results suggest linkage between cannabinoid pathway loci and highlight the need for further detailed characterisation of cannabinoid inheritance to facilitate metabolic engineering of chemically elite germplasm.

Recent advances in Cannabis sativa genomics research

“…The differential expression of CsTPS genes among cultivars also has been linked to variation in terpene profiles of these cultivars (Booth et al ., 2020). However, the genes underlying the synthesis of many minor cannabinoids and associated expression patterns are less well‐defined (Pollastro et al ., 2011; Citti et al ., 2019; Welling et al ., 2019; Basas‐Jaumandreu & de las Heras, 2020).…”

Season‐long characterization of high‐cannabinoid hemp (Cannabis sativa L.) reveals variation in cannabinoid accumulation, flowering time, and disease resistance

“…Despite recent genetic studies that have characterized the complex arrangement of the CBDAS (cannabidiolic acid synthase) and THCAS (tetrahydrocannabinolic acid synthase) genes at the B locus (Grassa et al, 2018; Laverty et al, 2019), they can largely be modeled as a single allelic locus because the THCAS and CBDAS genes are tightly linked in repulsion. The classification scheme for the five common chemotypes (Table 1) does not incorporate variation in abundance of propyl cannabinoids, CBC (cannabichromene), or less common alleles at the B locus (de Meijer, Hammond, & Micheler, 2009; Onofri et al, 2015; Welling et al, 2019). de Meijer and Hammond (2016) proposed a more complete model of inheritance, including the postulated polygenic loci A 1− n , controlling abundance of propyl cannabinoids, and PJC 1− n , controlling a set of morphological factors conferring a “prolonged juvenile chemotype” with a greater proportion of CBC.…”

An extreme-phenotype genome‐wide association study identifies candidate cannabinoid pathway genes in Cannabis

“…Resequencing of pools divergent for both CBDA and THCVA allowed genetic characterisation of two distinct chemotypes, resulting in the detection of trait-associated variants within a candidate gene putative linked to alkyl cannabinoid synthesis. This study made use of rare allelic variation present within a subset of the Cannabis genepool and highlights the importance of ex situ germplasm conservation and the systematic phenotyping of these resources for genetic improvement 50 , 81 .…”