6.1. The evolutionary and developmental importance of flowering time

Flowering time control is essential for reproductive success (Shim et al., 2017). Mechanisms to control the time of flowering have evolved given the negative consequences of spontaneous floral initiation: Premature flowering could coincide with the absence of pollinators or dispersers, subsequently causing reduced fertilisation rates and deficient seed dispersal. Conversely, if flowering occurs too late the plant may fail to set seed before harsh conditions hit at the end of the growing season (Gaudinier and Blackman, 2020). Moreover, in dioecious species such asCannabis , the timing of flower emergence is particularly crucial, because if male and female plants do not flower concurrently, pollination cannot occur (Hall et al., 2012). Hence it is evolutionarily beneficial for plants to possess mechanisms to fine-tune their floral initiation (Gaudinier and Blackman, 2020). Analyses in various plant species have demonstrated that flowering time in angiosperms is controlled by internal timekeeping mechanisms as well as environmental signals. Among the major factors controlling flowering time are the plant age, the photoperiod, the circadian clock, ambient temperature, the phytohormone gibberellin and the autonomous pathway (Fornara et al., 2010; Hill and Li, 2016).
The fine-tuning of flowering time is a major goal for plant breeding and crop improvement efforts. Floral transition represents the developmental shift from vegetative to reproductive growth and is a major determinant of yield potential (Jung and Müller, 2009). Alterations in key flowering time genes have been crucial to crop domestication, facilitating the adaptation of crops to local climatic conditions (Gaudinier and Blackman, 2020; Schilling et al., 2018). The success and worldwide expansion of staple crops like wheat and rice can partly be attributed to natural variation in flowering time genes, which enabled local adaptation for cultivation at a wide range of latitudes (Hill and Li, 2016; Langer et al., 2014). As a quantitative short-day plant, Cannabis flowering time is particularly determined by the photoperiod. Under long-days Cannabis remains vegetative and flowering is only induced when a number of short-day photoperiods have passed. Therefore, in order to cultivate Cannabis at new lines of latitude (for example in Ireland where summer daylengths can be over 17h), the adjustment of flowering time genes can be advantageous. Consequently, comprehensive characterisation of the Cannabis flowering time pathways is crucial to the integration of this crop species into modern agriculture.