Under natural conditions plants co-ordinate flowering with prevailing seasonal conditions to maximize reproductive success. Man has exploited natural variation in flowering time to produce crop plants adapted to conditions in the field to guarantee timely ripening, reduce exposure to seasonal environmental stresses, and increase yield. However, since the 1990s the yield increase rates for major food staples like wheat and rice have been declining. There is widespread concern that we are approaching the yield barriers of many crop species, thus necessitating new technologies and visions for crop improvement both to safeguard food supply and to satisfy increasing demands for plant biomass as a source of renewable energy.
Critical time points in determining the extent of reproductive growth and, thus, yield potential, are the induction of floral transition, the onset of flowering and the end of flowering (duration of flowering). These time points are genetically controlled and depend on environmental cues such as changes in temperature or photoperiod and abiotic stress, e.g. drought. In nature, phenological shifts in response to these cues are critical for adaptation to changing environmental conditions. The phenological development of a plant is highly important also for crop breeding. The timing of flowering and a plant's requirement for and responsiveness to vernalization are major factors in regional climatic adaptation of elite germplasm. The global climate change creates new challenges for breeders. Understanding how plants react to changing environmental conditions is important for knowledge-based breeding of better adapted crops or to introduce new crops species. For example, changing the time of flowering is an important means to avoid drought conditions. Warmer winters may also cause loss of adequate vernalization response of crops when grown in certain latitudes.
In all seed crops floral transition is a key developmental switch that determines the production of dry matter. In vegetative crops like cabbage, sugar beet or fodder grasses, early bolting and flowering can limit the potential for yield increases or interfere with harvest operations. In many trees and other perennials, breeding progress is severely hampered by the late onset of flowering. There is also increasing evidence that FTi genes have pleiotropic effects and do not only determine FTi, but also have a more general impact on plant morphology such as branching and number of flowers1. Furthermore, it was recently reported that genes that control FTi affect hybrid vigor and thus are likely to impact on yield also through this - for crop improvement highly important - genetic phenomenon.
The knowledge from model plants, together with the newly emerging genomic tools (e.g. whole genome sequences) for crop species, offers an excellent opening to a new dimension of integrated research as discussed at an international meeting in 2008 entitled “Control of flowering time and applications for plant breeding”. This meeting was organized by the coordinator of this SPP proposal. This research aims to gain a deep understanding of the regulators of FTi control beyond model species. The comparative analysis of floral transition regulatory networks between multiple species within the framework of this program importantly is also expected to help identify distinct evolutionary paths, dead ends, and byroads towards optimization of FTi regulation in the diverse set of species under study, and the branching points where these paths may have diverged.
1. Shalit,A. et al. (2009) The flowering hormone florigen functions as a general systemic regulator of growth and termination. Proceedings of the National Academy of Sciences of the USA 106, 8392-8397