What makes trichomes tick? Understanding the regulation of Cannabis (Cannabis sativa L.) glandular trichomes and their associated metabolism
Creators: name: Dimopoulos, Nicolas
Publisher: name: Southern Cross University
Year: 2024
Subjects: Cannabis sativa
Trichome
Glandular trichome
Cannabinoids
Terpenoids
Quantitative proteomics
SWATH-MS
Phytohormones
Drought stress
Jasmonic acid
Salicylic acid
Cytokinin
Abscisic acid
Central carbon metabolism
Secondary metabolism
Development
Photoassimilates
Diurnal
Circadian
Daytime

description: Hair-like glandular trichomes (GT) on female Cannabis (Cannabis sativa L.) reproductive organs are major sites of cannabinoid and terpenoid production and storage. GTs are highly differentiated organs that undergo modification of their programming, metabolism and structure. Evidence from other species suggests that regulation of GT development and metabolism are influenced by phytohormones and the environment. Yet, it is not understood how these factors regulate mature Cannabis GTs. Through a series of three studies, this thesis aims to unravel the roles of the diurnal cycle, phytohormones and drought stress on Cannabis GT regulation and productivity, and how cannabinoids and terpenoids change.
description: Cannabis GTs are non-photosynthetic with their primary metabolism modified to directly feed into secondary metabolism, making them strong sink tissues. By relying on photoassimilates from source tissues that fluctuate with the circadian rhythm, the first study investigated if GT secondary metabolism fluctuates over the light period. Results found that in planta, cannabinoid content increased with daytime progression, which correlated with increases in glycolytic enzymes in the GT despite a decrease in cannabinoid biosynthetic proteins. This indicated that daytime increases of photoassimilates are a main driver of cannabinoid productivity.
description: The second study investigated the role of plant phytohormones on GT secondary metabolite biosynthesis and accumulation in vitro. The effects of eight different phytohormones on the proteome and metabolome of isolated trichomes were tested. The assay showed that jasmonic acid (JA), salicylic acid (SA) and cytokinins had the largest impacts on the GT proteome and induced common responses. Trichome developmental processes were upregulated, and aspects of primary metabolism were downregulated. Neither cannabinoid biosynthetic proteins nor cannabinoid content were altered by the hormone application in vitro, suggesting that in planta increases previously shown for JA and SA, may be due to increased GT density or altered source-sink relationships.
description: The third study compared the effects of short-term drought and abscisic acid (ABA) application on the GT proteome and metabolome in planta. Drought stress during late flowering has been shown to increase cannabinoid content. Both drought and ABA treatment induced similar cellular stress responses, indicating ABA’s important role in GT drought response. Neither drought nor ABA increased proteins involved in secondary metabolite synthesis, contrary to the increase in cannabinoids due to drought. This would imply changes in photoassimilate availability to the GT during drought stress.
description: This thesis provides insights into how phytohormones and environmental changes regulate the primary and secondary metabolism of cannabis glandular trichomes.