Understanding flowering time.

Abstract The timing of the onset of flowering can be critical for the competence and survival of a plant species in particular environments. Regulation of flowering time in plants involves complex interactions between several endogenous and environmental factors. During post-embryonic growth, plants undergo two significant developmental transitions that impact on flowering time. The first occurs during vegetative growth when plants switch from a juvenile to an adult (or mature) phase of growth, referred to as vegetative phase change or vegetative maturation. The onset of maturity brings about reproductive competence and the second transition involves a switch within the shoot apical meristem (SAM) from a programme of vegetative to floral development. This floral transition is regulated by the complex interaction of components that either repress or promote flowering involved in largely four main floral input pathways: the photoperiodic, autonomous, gibberellin (GA) and vernalization pathways. The juvenile-to-adult transition within the vegetative phase and the vegetative to reproductive transition are independently regulated and yet coordinated processes. The precise timing of the onset of flowering in any given environmental condition is influenced by the time taken to proceed through both developmental transitions. Over recent years, there have been significant advances in our understanding of the regulation of flowering time. This review summarizes the current knowledge gained from classical physiological and contemporary molecular and genetic studies carried out on model flowering plants.