Non-photoperiodic transition of female cannabis seedlings from juvenile to adult reproductive stage.

KEY MESSAGE: Vegetative-to-reproductive phase transition in female cannabis seedlings occurs autonomously with the de novo development of single flowers. To ensure successful sexual reproduction, many plant species originating from seedlings undergo juvenile-to-adult transition. This phase transition precedes and enables the vegetative-to-reproductive shift in plants, upon perception of internal and/or external signals such as temperature, photoperiod, metabolite levels, and phytohormones. This study demonstrates that the juvenile seedlings of cannabis gradually shift to the adult vegetative stage, as confirmed by the formation of lobed leaves, and upregulation of the phase-transition genes. In the tested cultivar, the switch to the reproductive stage occurs with the development of a pair of single flowers in the 7th node. Histological analysis indicated that transition to the reproductive stage is accomplished by the de novo establishment of new flower meristems which are not present in a vegetative stage, or as dormant meristems at nodes 4 and 6. Moreover, there were dramatic changes in the transcriptomic profile of flowering-related genes among nodes 4, 6, and 7. Downregulation of flowering repressors and an intense increase in the transcription of phase transition-related genes occur in parallel with an increase in the transcription of flowering integrators and meristem identity genes. These results support and provide molecular evidence for previous findings that cannabis possesses an autonomous flowering mechanism and the transition to reproductive phase is controlled in this plant mainly by internal signals.