The genetic basis of flowering responses to seasonal cues

Key Points 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. Seasonal cues, such as day length and temperature, influence the developmental programme of plants. Recent genetic research has shed light on the pathways that lead to seasonal responses in flowering. The regulation of these pathways in Arabidopsis thaliana , their conservation throughout other species and comparative analysis of annual and perennial plants are considered here. Plants respond to the changing seasons to initiate developmental programmes precisely at particular times of year. Flowering is the best characterized of these seasonal responses, and in temperate climates it often occurs in spring. Genetic approaches in Arabidopsis thaliana have shown how the underlying responses to changes in day length (photoperiod) or winter temperature (vernalization) are conferred and how these converge to create a robust seasonal response. Recent advances in plant genome analysis have demonstrated the diversity in these regulatory systems in many plant species, including several crops and perennials, such as poplar trees. Here, we report progress in defining the diverse genetic mechanisms that enable plants to recognize winter, spring and autumn to initiate flower development.