Cannabis leaf arrangement: Transcriptome insights into Cannabis sativa phyllotactic regulation

Cannabis sativa exhibits notable phyllotactic transitions from opposite to alternate leaf arrangements, frequently coinciding with the shift from vegetative to reproductive growth. Yet, the regulatory mechanisms governing phyllotactic changes in cannabis remain understudied. This study thus seeks to investigate the transcriptomic changes that underpin this transition by comparing tissues from three nodes representing various stages of growth (i.e., nodes 6 and 11 displaying opposite phyllotaxy, and node 12 exhibiting alternate phyllotaxy). Among the 17,293 expressed genes detected, our analysis revealed that 6878 were differentially expressed genes (DEGs). Moreover, our analysis identified transcripts encoding a variety of transcription factors linked to either the holistic development of the shoot apical meristem (e.g., WRKY, bHLH, and MYB) or specific hormone signalling pathways (e.g., bZIP, TCP, MADS-box, AP2-ERE, and ARF). A total of 50 and 28 DEGs were identified and linked to the auxin and cytokinin pathways, respectively, recognized as the two most crucial phytohormones influencing phyllotaxis. Moreover, notable variations in gene expression patterns were evident in several genes (e.g., LAX, PIN, ARF, YUC, CLV3) known for their functional roles in phyllotaxy alterations in Arabidopsis. These genes exhibited distinct expression profiles during the transition from opposite to alternate arrangements in cannabis. Additionally, 1115 DEGs remained uncharacterized (unknown function) and might be novel genes involved in phyllotactic development. Generally, the results of this study offer novel insights into the mechanisms governing phyllotaxy pattern development, contributing to an enhanced understanding of how gene expression changes determine the phyllotaxy transition in cannabis.