The genetic basis of flowering responses to seasonal cues

Day length and temperature are the major seasonal cues that regulate flowering, and molecular pathways conferring these responses have been defined in Arabidopsis thaliana and several other species.Day length is measured in the leaves, and in all species examined it causes expression of highly conserved genes similar to FT of A. thaliana.In many species, a graft-transmissible signal that includes the FT protein is made in the leaves in response to day length and is transported to the shoot apical meristem, where it induces the floral transition.Seasonal flowering is also controlled by extended exposure to low winter temperatures (vernalization) that confers competence to flower in response to day length the following summer and spring.Genetic networks that confer vernalization appear to have evolved independently in different plant families and are therefore an example of convergent evolution.In contrast to annual plants, perennial plants flower multiple times during their lifespan. Recently developed genetic models for perennial species have identified floral repressors that are regulated by environmental signals and differentially expressed compared with closely related annual species.