## 4 Jasmonates: Biosynthesis, Signaling, and Functions
### Deeper Mechanistic Insights: How MeJA Modulates Trichome Development and Cannabinoid Biosynthesis
#### 4.2.5 Crosstalk with Other Hormones at the Molecular Level  
Gibberellins (GA) typically promote growth and biomass accumulation, whereas jasmonates, such as MeJA, shift resource allocation toward defense and secondary metabolism. In cannabis, MeJA drives the expression of GA2-oxidases, which degrade active GA, causing DELLA proteins to accumulate and hinder GA-responsive genes [46; 57]. This process results in shorter internodes and reduced overall biomass, but it promotes enhanced trichome formation and the accumulation of secondary metabolites. For indoor or vertical cultivation, reduced plant stature may be advantageous when paired with elevated cannabinoid production, illustrating how GA-JA antagonism can be harnessed to optimize yield and space management.  
Salicylic acid (SA) is generally associated with defense against biotrophic pathogens, whereas jasmonic acid (JA) and MeJA are more effective against herbivores and heterotrophic pathogens [45]. Although both SA and MeJA can independently raise cannabinoid levels in cannabis, the combination or sequential application of these hormones remains insufficiently explored [51]. High levels of SA often downregulate certain JA-responsive genes through WRKY transcription factors or NPR1-mediated pathways, potentially constraining MeJA-induced increases in trichome density [58; 59]. Conversely, heightened JA/MeJA signaling can suppress some SA-linked defenses, which might influence susceptibility to biotrophic pathogens. These dynamics highlight the importance of carefully managing timing and dosages if SA and MeJA are to be used together in integrated pest management strategies for cannabis.  
Ethylene (ET) can strengthen JA responses, especially in defending against necrotrophic pathogens. In cannabis, ET is best known for its role in sex expression, particularly in encouraging female flower development. Nevertheless, there is a theoretical possibility that ET and MeJA co-activation could heighten the expression of certain defense genes, such as PDF1.2, and accelerate shifts toward trichome-based defenses [60]. Although direct evidence on cannabis remains sparse, co-applying MeJA with an ethylene precursor (for instance, ACC) may intensify certain stress-induced phenotypes and further increase resin production. Such synergy could become a valuable horticultural tool, though excessive hormone exposure must be avoided to prevent yield penalties or unintentional stress responses. By integrating these perspectives on JA-GA antagonism, JA-SA trade-offs, and JA-ET synergy, it becomes clear that MeJA is only one component within a complex hormonal network that regulates plant growth and defense. In cannabis, the net effects of MeJA on trichome formation and cannabinoid production depend substantially on interactions with other signaling molecules. This understanding supports the idea that, with careful timing and precise application, MeJA can be strategically employed to bolster trichome-based chemical defenses and elevate the overall yield of medically and commercially valuable cannabinoids.