Characterization of the Cannabis sativa glandular trichome proteome

Building a biofactory: Constructing glandular trichomes in Cannabis sativa

Flowers of Cannabis sativa L. are densely covered with glandular trichomes containing cannabis resin that is used for medicinal and recreational purposes. The highly productive glandular trichomes have been described as 'biofactories.' In this review, we use this analogy to highlight recent advances in cannabis cell biology, metabolomics, and transcriptomics. The biofactory is built by epidermal outgrowths that differentiate into peltate-like glandular trichome heads, consisting of a disc of interconnected secretory cells with unique cellular structures. Cannabinoid and terpenoid products are warehoused in the extracellular storage cavity. Finally, multicellular stalks raise the glandular heads above the epidermis, giving cannabis flower their frosty appearance.

Grafting of Cannabis - The effect of the rootstock on vegetative and reproductive indices of the scion

Among the commercial cannabis varieties, some are high yielders but characterized by a relatively poor root system. Roots absorb water and minerals from the soil, enabling vegetative development that directly affects yield, as vigorous plants have more resources to support reproduction. Moreover, healthy foliage is a primary key to high assimilation rates, leading to better production of photosynthetic products, including cannabinoids and terpenes, which are the main active components of cannabis. We grafted a high-THC variety, named 'Freud Super-Ego' (FSE) onto three chemotypes of rootstocks: high-THC (T), high-CBD (C), and Balanced (B). All the rootstocks had significantly greater root biomass compared to FSE. All the grafting treatments significantly improved FSE's vegetative indices and yield. The best overall vegetative performance - height, stem circumference, number of mature leaves - was that of plants grafted onto the Balanced and high-CBD rootstocks, resulting in high yields as well. However, the greatest number of inflorescences was counted when FSE was grafted onto a high-THC rootstock. According to leaf mineral content analysis, the highest nitrogen and phosphorus levels were found in leaves of FSE grafted on the balanced rootstock. The cannabinoid content profile analysis revealed that all grafting treatments raised the THC level in FSE's inflorescences by 8-12% in comparison to the non-grafted control, and the THC rootstock led to the highest THC level. The results indicate the importance of grafting in cannabis as a tool to increase the productivity and quality of the product.

Charting the Cannabis plant chemical space with computational metabolomics

INTRODUCTION

The chemical classification of Cannabis is typically confined to the cannabinoid content, whilst Cannabis encompasses diverse chemical classes that vary in abundance among all its varieties. Hence, neglecting other chemical classes within Cannabis strains results in a restricted and biased comprehension of elements that may contribute to chemical intricacy and the resultant medicinal qualities of the plant.

OBJECTIVES

Thus, herein, we report a computational metabolomics study to elucidate the Cannabis metabolic map beyond the cannabinoids.

METHODS

Mass spectrometry-based computational tools were used to mine and evaluate the methanolic leaf and flower extracts of two Cannabis cultivars: Amnesia haze (AMNH) and Royal dutch cheese (RDC).

RESULTS

The results revealed the presence of different chemical compound classes including cannabinoids, but extending it to flavonoids and phospholipids at varying distributions across the cultivar plant tissues, where the phenylpropnoid superclass was more abundant in the leaves than in the flowers. Therefore, the two cultivars were differentiated based on the overall chemical content of their plant tissues where AMNH was observed to be more dominant in the flavonoid content while RDC was more dominant in the lipid-like molecules. Additionally, in silico molecular docking studies in combination with biological assay studies indicated the potentially differing anti-cancer properties of the two cultivars resulting from the elucidated chemical profiles.

CONCLUSION

These findings highlight distinctive chemical profiles beyond cannabinoids in Cannabis strains. This novel mapping of the metabolomic landscape of Cannabis provides actionable insights into plant biochemistry and justifies selecting certain varieties for medicinal use.

The putative cannabinoid-secreting trichome of Trema micrantha (L.) Blume (Cannabaceae)

Trema, a genus of the popularly known Cannabaceae, has recently been the subject of cannabinoid bioprospection. T. micrantha is a tree with pharmacological potential widely used in folk medicine. It has two types of glandular trichomes, bulbous and filiform, spread throughout the plant body. Considering the proximity of this species to Cannabis sativa and Trema orientalis, species containing cannabinoids, the glandular trichomes of T. micrantha are also expected to be related to the secretion of these compounds. Thus, this study aims to detail the morphology of secretory trichomes during the synthesis, storing and release of metabolites in T. micrantha. We tested the proposition that they could be a putative type of cannabinoid-secreting gland. Pistillate and staminate flowers and leaves were collected and processed for ontogenic, histochemical, and ultrastructural analyses. Both types of glandular trichomes originate from a protodermal cell. They are putative cannabinoid-secreting sites because: (1) terpene-phenols and, more specifically, cannabinoids were detected in situ; (2) their secretory subcellular apparatus is consistent with that found in C. sativa: modified plastids, polyribosomes, an extensive rough endoplasmic reticulum, and a moniliform smooth endoplasmic reticulum. Plastids and smooth endoplasmic reticulum are involved in the synthesis of terpenes, while the rough endoplasmic reticulum acts in the phenolic synthesis. These substances cross the plasma membrane by exocytosis and are released outside the trichome through cuticle pores. The study of the cell biology of the putative cannabinoid glands can promote the advancement of prospecting for natural products in plants.

Quantitative Determination of Cannabis Terpenes Using Gas Chromatography-Flame Ionization Detector

Background: Cannabis has a long history of being credited with centuries of healing powers for millennia. The cannabis plant is a rich source of cannabinoids and terpenes. Each cannabis chemovar exhibits a different flavor and aroma, which are determined by its terpene content. Methods: In this study, a gas chromatography-flame ionization detector method was developed and validated for the determination of the 10 major terpenes in the main three chemovars of Cannabis sativa L. with n-tridecane used as the internal standard following the standard addition method. The 10 major terpenes (monoterpenes and sesquiterpenes) are α-pinene, β-pinene, β-myrcene, limonene, terpinolene, linalool, α-terpineol, β-caryophyllene, α-humulene, and caryophyllene oxide. The method was validated according to Association of Official Analytical Chemists guidelines. Spike recovery studies for all terpenes were carried out on placebo cannabis material and indoor-growing high THC chemovar with authentic standards. Results: The method was linear over the calibration range of 1-100 μg/mL with r2>0.99 for all terpenes. The limit of detection and limit of quantification were calculated to be 0.3 and 1.0 μg/mL, respectively, for all terpenes. The accuracy (%recovery) at all levels ranged from 89% to 104% and 90% to 111% for placebo and indoor-growing high THC chemovar, respectively. The repeatability and intermediate precision of the method were evaluated by the quantification of target terpenes in the three different C. sativa chemovars, resulting in acceptable relative standard deviations (less than 10%). Conclusions: The developed method is simple, sensitive, reproducible, and suitable for the detection and quantification of monoterpenes and sesquiterpenes in C. sativa biomass.

Shifts in carbon partitioning by photosynthetic activity increase terpenoid synthesis in glandular trichomes

Several commercially important secondary metabolites are produced and accumulated in high amounts by glandular trichomes, giving the prospect of using them as metabolic cell factories. Due to extremely high metabolic fluxes through glandular trichomes, previous research focused on how such flows are achieved. The question regarding their bioenergetics became even more interesting with the discovery of photosynthetic activity in some glandular trichomes. Despite recent advances, how primary metabolism contributes to the high metabolic fluxes in glandular trichomes is still not fully elucidated. Using computational methods and available multi-omics data, we first developed a quantitative framework to investigate the possible role of photosynthetic energy supply in terpenoid production and next tested experimentally the simulation-driven hypothesis. With this work, we provide the first reconstruction of specialised metabolism in Type-VI photosynthetic glandular trichomes of Solanum lycopersicum. Our model predicted that increasing light intensities results in a shift of carbon partitioning from catabolic to anabolic reactions driven by the energy availability of the cell. Moreover, we show the benefit of shifting between isoprenoid pathways under different light regimes, leading to a production of different classes of terpenes. Our computational predictions were confirmed in vivo, demonstrating a significant increase in production of monoterpenoids while the sesquiterpenes remained unchanged under higher light intensities. The outcomes of this research provide quantitative measures to assess the beneficial role of chloroplast in glandular trichomes for enhanced production of secondary metabolites and can guide the design of new experiments that aim at modulating terpenoid production.

Hormonal control of promoter activities of Cannabis sativa prenyltransferase 1 and 4 and salicylic acid mediated regulation of cannabinoid biosynthesis

Cannabis sativa aromatic prenyltransferase 4 (CsPT4) and 1 (CsPT1) have been shown to catalyze cannabigerolic acid (CBGA) biosynthesis, a step that rate-limits the cannabinoid biosynthetic pathway; both genes are highly expressed in flowers. CsPT4 and CsPT1 promoter driven β-glucuronidase (GUS) activities were detected in leaves of cannabis seedlings, and strong CsPT4 promoter activities were associated with glandular trichomes. Hormonal regulation of cannabinoid biosynthetic genes is poorly understood. An in silico analysis of the promoters identified putative hormone responsive elements. Our work examines hormone-responsive elements in the promoters of CsPT4 and CsPT1 in the context of physiological responses of the pathway to the hormone in planta. Dual luciferase assays confirmed the regulation of promoter activities by the hormones. Further studies with salicylic acid (SA) demonstrated that SA pretreatment increased the expression of genes located downstream of the cannabinoid biosynthetic pathway. The results from all aspects of this study demonstrated an interaction between certain hormones and cannabinoid synthesis. The work provides information relevant to plant biology, as we present evidence demonstrating correlations between molecular mechanisms that regulate gene expression and influence plant chemotypes.

Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences

BACKGROUND

Glandular capitate trichomes which form on bract tissues of female inflorescences of high THC-containing Cannabis sativa L. plants are important sources of terpenes and cannabinoids. The influence of plant age and cannabis genotype on capitate trichome development, morphology, and maturation has not been extensively studied. Knowledge of the various developmental changes that occur in trichomes over time and the influence of genotype and plant age on distribution, numbers, and morphological features should lead to a better understanding of cannabis quality and consistency.

METHODS

Bract tissues of two genotypes-"Moby Dick" and "Space Queen"-were examined from 3 weeks to 8 weeks of flower development using light and scanning electron microscopy. Numbers of capitate trichomes on upper and lower bract surfaces were recorded at different positions within the inflorescence. Observations on distribution, extent of stalk formation, glandular head diameter, production of resin, and extent of dehiscence and senescence were made at various time points. The effects of post-harvesting handling and drying on trichome morphology were examined in an additional five genotypes.

RESULTS

Two glandular trichome types-bulbous and capitate (sessile or stalked)-were observed. Capitate trichome numbers and stalk length were significantly (P = 0.05) greater in "Space Queen" compared to "Moby Dick" at 3 and 6 weeks of flower development. Significantly more stalked-capitate trichomes were present on lower compared to upper bract surfaces at 6 weeks in both genotypes, while sessile-capitate trichomes predominated at 3 weeks. Epidermal and hypodermal cells elongated to different extents during stalk formation, producing significant variation in length (from 20 to 1100 μm). Glandular heads ranged from 40 to 110 μm in diameter. Maturation of stalked-capitate glandular heads was accompanied by a brown color development, reduced UV autofluorescence, and head senescence and dehiscence. Secreted resinous material from glandular heads appeared as droplets on the cuticular surface that caused many heads to stick together or collapse. Trichome morphology was affected by the drying process.

CONCLUSION

Capitate trichome numbers, development, and degree of maturation were influenced by cannabis genotype and plant age. The observations of trichome development indicate that asynchronous formation leads to different stages of trichome maturity on bracts. Trichome stalk lengths also varied between the two genotypes selected for study as well as over time. The variability in developmental stage and maturation between genotypes can potentially lead to variation in total cannabinoid levels in final product. Post-harvest handling and drying were shown to affect trichome morphology.

Metabolomic analysis of methyl jasmonate treatment on phytocannabinoid production in Cannabis sativa

Cannabis sativa is a multi-use and chemically complex plant which is utilized for food, fiber, and medicine. Plants produce a class of psychoactive and medicinally important specialized metabolites referred to as phytocannabinoids (PCs). The phytohormone methyl jasmonate (MeJA) is a naturally occurring methyl ester of jasmonic acid and a product of oxylipin biosynthesis which initiates and regulates the biosynthesis of a broad range of specialized metabolites across a number of diverse plant lineages. While the effects of exogenous MeJA application on PC production has been reported, treatments have been constrained to a narrow molar range and to the targeted analysis of a small number of compounds. Using high-resolution mass spectrometry with data-dependent acquisition, we examined the global metabolomic effects of MeJA in C. sativa to explore oxylipin-mediated regulation of PC biosynthesis and accumulation. A dose-response relationship was observed, with an almost two-fold increase in PC content found in inflorescences of female clones treated with 15 mM MeJA compared to the control group. Comparison of the inflorescence metabolome across MeJA treatments coupled with targeted transcript analysis was used to elucidate key regulatory components contributing to PC production and metabolism more broadly. Revealing these biological signatures improves our understanding of the role of the oxylipin pathway in C. sativa and provides putative molecular targets for the metabolic engineering and optimization of chemical phenotype for medicinal and industrial end-uses.

Moving Away from 12:12; the Effect of Different Photoperiods on Biomass Yield and Cannabinoids in Medicinal Cannabis

The standard practice to initiate flowering in medicinal cannabis involves reducing the photoperiod from a long-day period to an equal duration cycle of 12 h light (12L)/12 h dark (12D). This method reflects the short-day flowering dependence of many cannabis varieties but may not be optimal for all. We sought to identify the effect of nine different flowering photoperiod treatments on the biomass yield and cannabinoid concentration of three medicinal cannabis varieties. The first, "Cannatonic", was a high cannabidiol (CBD)-accumulating line, whereas the other two, "Northern Lights" and "Hindu Kush", were high Δ9-tetrahydrocannabinol (THC) accumulators. The nine treatments tested, following 18 days under 18 h light/6 h dark following cloning and propagation included a standard 12L:12D period, a shortened period of 10L:14D, and a lengthened period of 14L:10D. The other six treatments started in one of the aforementioned and then 28 days later (mid-way through flowering) were switched to one of the other treatments, thus causing either an increase of 2 or 4 h, or a decrease of 2 or 4 h. Measured parameters included the timing of reproductive development; the dry weight flower yield; and the % dry weight of the main target cannabinoids, CBD and THC, from which the total g cannabinoid per plant was calculated. Flower biomass yields were highest for all lines when treatments started with 14L:10D; however, in the two THC lines, a static 14L:10D photoperiod caused a significant decline in THC concentration. Conversely, in Cannatonic, all treatments starting with 14L:10D led to a significant increase in the CBD concentration, which led to a 50-100% increase in total CBD yield. The results show that the assumption that a 12L:12D photoperiod is optimal for all lines is incorrect as, in some lines, yields can be greatly increased by a lengthened light period during flowering.

Using a global diversity panel of Cannabis sativa L. to develop a near InfraRed-based chemometric application for cannabinoid quantification

C. sativa has gained renewed interest as a cash crop for food, fibre and medicinal markets. Irrespective of the final product, rigorous quantitative testing for cannabinoids, the regulated biologically active constituents of C. sativa, is a legal prerequisite across the supply chains. Currently, the medicinal cannabis and industrial hemp industries depend on costly chromatographic analysis for cannabinoid quantification, limiting production, research and development. Combined with chemometrics, Near-InfraRed spectroscopy (NIRS) has potential as a rapid, accurate and economical alternative method for cannabinoid analysis. Using chromatographic data on 12 therapeutically relevant cannabinoids together with spectral output from a diffuse reflectance NIRS device, predictive chemometric models were built for major and minor cannabinoids using dried, homogenised C. sativa inflorescences from a diverse panel of 84 accessions. Coefficients of determination (r²) of the validation models for 10 of the 12 cannabinoids ranged from 0.8 to 0.95, with models for major cannabinoids showing best performance. NIRS was able to discriminate between neutral and acidic forms of cannabinoids as well as between C₃-alkyl and C₅-alkyl cannabinoids. The results show that NIRS, when used in conjunction with chemometrics, is a promising method to quantify cannabinoids in raw materials with good predictive results.

Emerging trends in genomic and epigenomic regulation of plant specialised metabolism

Regulation of specialised metabolism genes is multilayered and complex, influenced by an array of genomic, epigenetic and epigenomic mechanisms. Here, we review the most recent knowledge in this field, drawing from discoveries in several plant species. Our aim is to improve understanding of how plant genome structure and function influence specialised metabolism. We also highlight key areas for future exploration. Gene regulatory mechanisms influencing specialised metabolism include gene duplication and neo-functionalization, conservation of operon-like clusters of specialised metabolism genes, local chromatin modifications, and the organisation of higher order chromatin structures within the nucleus. Genomic and epigenomic research to-date in the discipline have focused on a relatively small number of plant species, primarily at whole organ or tissue level. This is largely due to the technical demands of the experimental methods needed. However, a high degree of cell-type specificity of function exists in specialised metabolism, driven by similarly specific gene regulation. In this review we focus on the genomic characteristics of genes that are found in different types of clusters within the genome. We propose that acquisition of cell-resolution epigenomic datasets in emerging models, such as the glandular trichomes of Cannabis sativa, will yield important advances. Data such as chromatin accessibility and histone modification profiles can pinpoint which regulatory sequences are active in individual cell types and at specific times in development. These could provide fundamental biological insight as well as novel targets for genetic engineering and crop improvement.

Negative Interactions Balance Growth and Defense in Plants Confronted with Herbivores or Pathogens

Plants have evolved a series of defensive mechanisms against pathogens and herbivores, but the defense response always leads to decreases in growth or reproduction, which has serious implications for agricultural production. Growth and defense are negatively regulated not only through metabolic consumption but also through the antagonism of different phytohormones, such as jasmonic acid (JA) and salicylic acid (SA). Meanwhile, plants can limit the expression of defensive metabolites to reduce the costs of defense by producing constitutive defenses such as glandular trichomes or latex and accumulating specific metabolites, determining the activation of plant defense or the maintenance of plant growth. Interestingly, plant defense pathways might be prepared in advance which may be transmitted to descendants. Plants can also use external organisms to protect themselves, thus minimizing the costs of defense. In addition, plant relatives exhibit cooperation to deal with pathogens and herbivores, which is also a way to regulate growth and defense.

Biosynthetic origins of unusual cannabimimetic phytocannabinoids in Cannabis sativa L: A review

Plants of Cannabis sativa L. (Cannabaceae) produce an array of more than 160 isoprenylated resorcinyl polyketides, commonly referred to as phytocannabinoids. These compounds represent molecules of therapeutic importance due to their modulation of the human endocannabinoid system (ECS). While understanding of the biosynthesis of the major phytocannabinoids Δ⁹-tetrahydrocannabinol (Δ⁹-THC) and cannabidiol (CBD) has grown rapidly in recent years, the biosynthetic origin and genetic regulation of many potentially therapeutically relevant minor phytocannabinoids remain unknown, which limits the development of chemotypically elite varieties of C. sativa. This review provides an up-to-date inventory of unusual phytocannabinoids which exhibit cannabimimetic-like activities and proposes putative metabolic origins. Metabolic branch points exploitable for combinatorial biosynthesis and engineering of phytocannabinoids with augmented therapeutic activities are also described, as is the role of phytocannabinoid remodelling to accelerate the therapeutic portfolio expansion in C. sativa.

Plant Proteome Dynamics

Proteins are intimately involved in executing and controlling virtually all cellular processes. To understand the molecular mechanisms that underlie plant phenotypes, it is essential to investigate protein expression, interactions, and modifications, to name a few. The proteome is highly dynamic in time and space, and a plethora of protein modifications, protein interactions, and network constellations are at play under specific conditions and developmental stages. Analysis of proteomes aims to characterize the entire protein complement of a particular cell type, tissue, or organism-a challenging task, given the dynamic nature of the proteome. Modern mass spectrometry-based proteomics technology can be used to address this complexity at a system-wide scale by the global identification and quantification of thousands of proteins. In this review, we present current methods and technologies employed in mass spectrometry-based proteomics and provide examples of dynamic changes in the plant proteome elucidated by proteomic approaches.

Control of resource allocation between primary and specialized metabolism in glandular trichomes

Plant specialized metabolites are often synthesized and stored in dedicated morphological structures such as glandular trichomes, resin ducts, or laticifers where they accumulate in large concentrations. How this high productivity is achieved is still elusive, in particular, with respect to the interface between primary and specialized metabolism. Here, we focus on glandular trichomes to survey recent progress in understanding how plant metabolic cell factories manage to balance homeostasis of essential central metabolites while producing large quantities of compounds that constitute a metabolic sink. In particular, we review the role of gene duplications, transcription factors and photosynthesis.

Coenzymes and the primary and specialized metabolism interface

In plants, primary and specialized metabolism have classically been distinguished as either essential for growth or required for survival in a particular environment. Coenzymes (organic cofactors) are essential for growth but their importance to specialized metabolism is often not considered. In line with the recent proposal of viewing primary and specialized metabolism as an integrated whole rather than segregated lots with a defined interface, we highlight here the importance of collating information on the regulation of coenzyme supply with metabolic demands using examples of vitamin B derived coenzymes. We emphasize that coenzymes can have enormous influence on the outcome of metabolic as well as engineered pathways and should be taken into account in the era of synthetic biology.

Applications of cell- and tissue-specific 'omics to improve plant productivity

The individual tissues and cell types of plants each have characteristic properties that contribute to the function of the plant as a whole. These are reflected by unique patterns of gene expression, protein and metabolite content, which enable cell-type-specific patterns of growth, development and physiology. Gene regulatory networks act within the cell types to govern the production and activity of these components. For the broader organism to grow and reproduce successfully, cell-type-specific activity must also function within the context of surrounding cell types, which is achieved by coordination of signalling pathways. We can investigate how gene regulatory networks are constructed and function using integrative ‘omics technologies. Historically such experiments in plant biological research have been performed at the bulk tissue level, to organ resolution at best. In this review, we describe recent advances in cell- and tissue-specific ‘omics technologies that allow investigation at much improved resolution. We discuss the advantages of these approaches for fundamental and translational plant biology, illustrated through the examples of specialised metabolism in medicinal plants and seed germination. We also discuss the challenges that must be overcome for such approaches to be adopted widely by the community.

An advanced method for the release, enrichment and purification of high-quality Arabidopsis thaliana rosette leaf trichomes enables profound insights into the trichome proteome

BACKGROUND

Rosette leaf trichomes of Arabidopsis thaliana have been broadly used to study cell development, cell differentiation and, more recently, cell wall biogenesis. However, trichome-specific biochemical or -omics analyses require a proper separation of trichomes from residual plant tissue. Thus, different strategies were proposed in the past for trichome isolation, which mostly rely on harsh conditions and suffer from low yield, thereby limiting the spectrum of downstream analyses.

RESULTS

To take trichome-leaf separation to the next level, we revised a previously proposed method for isolating A. thaliana trichomes by optimizing the mechanical and biochemical specifications for trichome release. We additionally introduced a density gradient centrifugation step to remove residual plant debris. We found that prolonged, yet mild seedling agitation increases the overall trichome yield by more than 60% compared to the original protocol. We noticed that subsequent density gradient centrifugation further visually enhances trichome purity, which may be advantageous for downstream analyses. Gene expression analysis by quantitative reverse transcriptase-polymerase chain reaction validated a substantial enrichment upon purification of trichomes by density gradient centrifugation. Histochemical and biochemical investigation of trichome cell wall composition indicated that unlike the original protocol gentle agitation during trichome release largely preserves trichome integrity. We used enriched and density gradient-purified trichomes for proteomic analysis in comparison to trichome-depleted leaf samples and present a comprehensive reference data set of trichome-resident and -enriched proteins. Collectively we identified 223 proteins that are highly enriched in trichomes as compared to trichome-depleted leaves. We further demonstrate that the procedure can be applied to retrieve diverse glandular and non-glandular trichome types from other plant species.

CONCLUSIONS

We provide an advanced method for the isolation of A. thaliana leaf trichomes that outcompetes previous procedures regarding yield and purity. Due to the large amount of high-quality trichomes our method enabled profound insights into the so far largely unexplored A. thaliana trichome proteome. We anticipate that our protocol will be of use for a variety of downstream analyses, which are expected to shed further light on the biology of leaf trichomes in A. thaliana and possibly other plant species.

Cannabis Glandular Trichomes: A Cellular Metabolite Factory

Cannabis has been legalized for recreational use in several countries and medical use is authorized in an expanding list of countries; markets are growing internationally, causing an increase in demand for high quality products with well-defined properties. The key compounds of Cannabis plants are cannabinoids, which are produced by stalked glandular trichomes located on female flowers. These trichomes produce resin that contains cannabinoids, such as tetrahydrocannabinolic acid and cannabidiolic acid, and an array of other secondary metabolites of varying degrees of commercial interest. While growers tend to focus on improving whole flower yields, our understanding of the "goldmines" of the plant - the trichomes - is limited despite their being the true source of revenue for a multi-billion-dollar industry. This review aims to provide an overview of our current understanding of cannabis glandular trichomes and their metabolite products in order to identify current gaps in knowledge and to outline future research directions.

Genomic and Chemical Diversity of Commercially Available High-CBD Industrial Hemp Accessions

High consumer demand for cannabidiol (CBD) has made high-CBD hemp (Cannabis sativa) an extremely high-value crop. However, high demand has resulted in the industry developing faster than the research, resulting in the sale of many hemp accessions with inconsistent performance and chemical profiles. These inconsistencies cause significant economic and legal problems for growers interested in producing high-CBD hemp. To determine the genetic and phenotypic consistency in available high-CBD hemp varieties, we obtained seed or clones from 22 different named accessions meant for commercial production. Genotypes (∼48,000 SNPs) and chemical profiles (% CBD and THC by dry weight) were determined for up to 8 plants per accession. Many accessions-including several with the same name-showed little consistency either genetically or chemically. Most seed-grown accessions also deviated significantly from their purported levels of CBD and THC based on the supplied certificates of analysis. Several also showed evidence of an active tetrahydrocannabinolic acid (THCa) synthase gene, leading to unacceptably high levels of THC in female flowers. We conclude that the current market for high-CBD hemp varieties is highly unreliable, making many purchases risky for growers. We suggest options for addressing these issues, such using unique names and developing seed and plant certification programs to ensure the availability of high-quality, verified planting materials.