The on and off of floral regulatory genes

The development of a multicellular organism requires the cells to acquire increasingly restricted fates. Regulatory genes are needed to specify cell fates during development in both animals and plants. Many regulatory genes have defined temporal and spatial expression patterns; therefore, these genes are themselves highly regulated. Plant development is also controlled by the environment, and different environments can trigger alternative developmental pathways. One example is that the decision to commence reproductive development in plants is often regulated by day length, which signals seasonal changes. In the small weed Arabidopsis thaliana, long day photoperiods (LD, 16 hr light/8 hr dark) accelerate flowering, compared to short days (SD, 10 hr light/14 hr dark; Martinez-Zapater et al. 1994