Project description:BackgroundCannabis sativa cultivars can be classified as marijuana or hemp, depending on its amount of the psychoactive cannabinoid Δ9-tetrahydrocannabinolic acid (THCA). Hemp Cheungsam is a non-drug type Cannabis sativa that is characterized by low THCA content. However, the transcripts and expression profile of cannabinoid biosynthesis pathway genes of hemp Cheungsam have not been investigated.MethodsRNA-sequencing (RNA-seq) was performed on three different tissue types (flower, leaf, and stem) of hemp Cheungsam to understand their transcriptomes. The expression of cannabinoid biosynthesis pathway genes was further analyzed in each tissue type. Multiple sequence alignment and conserved domain analyses were used to investigate the homologs of cannbinoid biosynthesis genes.ResultsWe found that the cannabinoid biosynthesis pathway was mainly expressed in the flowers of hemp Cheungsam, similar to other Cannabis cultivars. However, expression of cannabidiolic acid (CBDA) synthase was much higher than THCA synthase and cannabichromenic acid (CBCA) synthase, suggesting that the transcription profile favors CBDA biosynthesis. Sequence analysis of cannabinoid biosynthesis pathway genes suggested the identity of orthologs in hemp Cheungsam.ConclusionsCannabinoid biosynthesis in hemp Cheungsam mostly occurs in the flowers, compared to other plant organs. While CBDA synthase expression is high, THCA and CBCA synthase expression is considerably low, indicating lesser THCA biosynthesis and thus low THCA content. Sequence analysis of key genes (CBDA, THCA, and CBCA synthases) of the cannabinoid biosynthetic pathway indicates that orthologs are present in hemp Cheungsam.
Project description:PremiseHow genetic variation within a species affects phytochemical composition is a fundamental question in botany. The ratio of two specialized metabolites in Cannabis sativa, tetrahydrocannabinol (THC) and cannabidiol (CBD), can be grouped into three main classes (THC-type, CBD-type, and intermediate type). We tested a genetic model associating these three groups with functional and nonfunctional alleles of the cannabidiolic acid synthase gene (CBDAS).MethodsWe characterized cannabinoid content and assayed CBDAS genotypes of >300 feral C. sativa plants in Minnesota, United States. We performed a test cross to assess CBDAS inheritance. Twenty clinical cultivars obtained blindly from the National Institute on Drug Abuse and 12 Canadian-certified grain cultivars were also examined.ResultsFrequencies of CBD-type, intermediate-type, and THC-type feral plants were 0.88, 0.11, and 0.01, respectively. Although total cannabinoid content varied substantially, the three groupings were perfectly correlated with CBDAS genotypes. Genotype frequencies observed in the test cross were consistent with codominant Mendelian inheritance of the THC:CBD ratio. Despite significant mean differences in total cannabinoid content, CBDAS genotypes blindly predicted the THC:CBD ratio among clinical cultivars, and the same was true for industrial grain cultivars when plants exhibited >0.5% total cannabinoid content.ConclusionsOur results extend the generality of the inheritance model for THC:CBD to diverse C. sativa accessions and demonstrate that CBDAS genotyping can predict the ratio in a variety of practical applications. Cannabinoid profiles and associated CBDAS segregation patterns suggest that feral C. sativa populations are potentially valuable experimental systems and sources of germplasm.
Project description:A comprehensive understanding of the degree to which genomic variation is maintained by selection versus drift and gene flow is lacking in many important species such as Cannabis sativa (C. sativa), one of the oldest known crops to be cultivated by humans worldwide. We generated whole genome resequencing data across diverse samples of feralized (escaped domesticated lineages) and domesticated lineages of C. sativa. We performed analyses to examine population structure, and genome wide scans for FST, balancing selection, and positive selection. Our analyses identified evidence for sub-population structure and further support the Asian origin hypothesis of this species. Feral plants sourced from the U.S. exhibited broad regions on chromosomes 4 and 10 with high F̄ST which may indicate chromosomal inversions maintained at high frequency in this sub-population. Both our balancing and positive selection analyses identified loci that may reflect differential selection for traits favored by natural selection and artificial selection in feral versus domesticated sub-populations. In the U.S. feral sub-population, we found six loci related to stress response under balancing selection and one gene involved in disease resistance under positive selection, suggesting local adaptation to new climates and biotic interactions. In the marijuana sub-population, we identified the gene SMALLER TRICHOMES WITH VARIABLE BRANCHES 2 to be under positive selection which suggests artificial selection for increased tetrahydrocannabinol yield. Overall, the data generated, and results obtained from our study help to form a better understanding of the evolutionary history in C. sativa.