Regulation framework for flowering

Plants are sessile organisms that have developed the ability to perceive, anticipate and respond to environmental changes to maximize their ability to survive and reproduce. One of the most important aims in the life of any plant is to flower and reproduce. Plants regulate the timing of the onset of flowering to enable seed production and dispersal before environmental conditions become too adverse. For outbreeding species flowering is often synchronised with other individuals, or with insect or bird pollinators, to increase the chance of cross-pollination. Furthermore, if a plant flowers too early it might not be sufficiently well established and lack enough resources to support the production of flowers and seed. Timing is therefore the key to success and plants have developed a very elaborate network of interact- ing molecular pathways to control when flowering occurs. These pathways are influenced by predictable environmental cues such as diurnal and annual changes in light and temperature, and by unpredictable and internal factors such as nutrient levels, biotic and abiotic stresses, plant age and maturity. Plants modulate their development in response to these factors with short term (eg. diurnal) or long term (eg. seasonal) responses accordingly. The rate of the response is also dependent on the plant species. Generally plants are divided between annual plants that complete their development within 1 year, flowering just once at the end of their life-cycle, and biennials or perennial plants whose life cycles span two or more years, during which they can flower once (monocarpic) or several times (polycarpic). From a farming point of view, understanding the flowering time process, antici- pating and controlling it is extremely important for crop scheduling and also because flowering influences yield. As flowering time is of such commercial impor- tance, a lot of research has been devoted to uncovering the genetic mechanisms underlying the various flowering pathways that affect flowering time. Using molec- ular genetic approaches in the annual model plant Arabidopsis thaliana, and in rice and other species, many components of these pathways have now been identified. In this chapter, the current understanding of the molecular pathways that plants use to respond to the external environmental and internal endogenous signals to regulate flowering is summarized. The flowering repressors that act to prevent plants from flowering until the right moment, and the floral integrator genes, which activate the floral meristem identity genes are described. The main focus is on what is known about the Arabidopsis flowering process, as this is the best understood model and there is a lot of available information, but what happens in other plants species will also be considered.