## 3 Discussion
### Jasmonic Acid Is a Key Coordinating Phytohormone for GT Initiation and Development in Cannabis  
Our study supports recent research that established JA signalling as a key regulatory pathway for the initiation, development, and function of cannabis glandular trichomes. While foliar application of JA caused increased cannabinoid content in floral tissue [28], this increase is unlikely due to upregulation of the cannabinoid biosynthetic pathway. CBGA synthesis is a likely rate-limiting step in the pathway [33] and is synthesised by two aromatic prenyltransferases: CsPT1 and CsPT4. The expression of these two enzymes has been found to be unresponsive to methyl jasmonate, and promoter regions of their genes do not have JA-responsive elements [39]. We similarly found that JA did not affect the abundance of CsPT1, tetraketide synthase, THCA synthase, or subunits of GPP synthase (GPPS.ssu and GPPS.lsu), while it caused a decrease in olivetolic acid cyclase and CBDA synthase (Figure 7). Congruently, exposure of GT disc cells to JA did not increase either CBGA or THCA content _in vitro_ (Figure 6A, B). Consequently, increased floral cannabinoid content _in planta_ by JA [28] may be caused by some mechanism other than upregulation of biosynthetic enzymes. This could either be by increasing the allocation of carbon to secondary metabolism, which some plants do when under stress [80], or by promoting GT initiation to increase overall floral GT density, a phenomenon recently observed in cannabis [29].  
[PERSON] et al. [29] found that a methyl jasmonate (MeJA) mediated pathway was involved in trichome formation. Foliar application of MeJA increased trichome density on cannabis flowers and RNA-Seq analysis detected a cluster of MeJA responsive genes that strongly correlated with GT formation during flower development. CsMYC4,a bHLH transcription factor (TF), was identified as a key regulatory gene in the cluster and is a close homolog of the trichome inducing SIMYC1 TF in tomato [81]. Consequently, [PERSON] et al. [29] proposed a MYC-JAZ complex as the JA induction mechanism for GT initiation. This is similar to the mechanism in tomato and artemisia [82] and the MBW model of multicellular trichome initiation [24]. Our research further substantiates [PERSON] et al.'s [29] findings that JA is important for cannabis GT development. We observed that 11.8% of quantified proteins responded to JA in mature GTs that were sampled at 6 weeks into flowering. As well, we found that treating GTs with DIECA likely inhibited the jasmonic acid pathway, which resulted in GTs showing signs of a stress response. These two observations indicated that mature GTs are receptive to jasmonic acid signalling past the trichome initiation stage, and that JA is likely important for maintaining GT homeostasis. Furthermore, JA regulated key proteins involved in leucoplast formation, cuticle and cell wall modification, and energy metabolism (via acetyl-CoA reallocation), which are processes needed for the development of mature cannabis GTs (Figure 8). Finally, the similarity of the KIN and SA responses to JA suggests a more complex integration of hormonal interplay to be of importance for GT homeostasis in cannabis.