Discriminating differences in day length is critical for many organisms to synchronize reproduction with the most favourable season of the year. Plants have evolved sophisticated time-keeping mechanisms that largely work in leaves, to measure the duration of the day. Upon perception of favourable day lengths, a leaf-borne signal moves to the shoot apical meristem to induce flower formation. Rice is a crop whose yield heavily depends on flowering at the right time, and genetic variation within leaf regulators contributes to diversification of flowering responses among different rice varieties. However, how the shoot apical meristem responds to changes in day length and initiates flowering is currently unknown. High-yielding European rice varieties flower within a limited range of days and expanding such range would prove beneficial to increase yield and expand cultivation to different environments. Our goal is to identify novel genes that modify meristem sensitivity to day length, and breed them into high-yielding cultivars. Together with the gene pool controlling day length responses in the leaves, these novel alleles will allow to design varieties with diverse sensitivities to photoperiod and will distribute the reproductive phase over a broader period of time. This knowledge-based breeding will require preliminary studies in order to identify regulators acting in the shoot apical meristem. To this extent, rice provides an excellent biological model for the availability of powerful genetic and molecular tools. I am proposing a number of genetic and biochemical screens that will allow us to explore the rice genome for genes required at the shoot apical meristem to drive reproductive phase transitions. We will investigate genetic variation in these components, relate it to flowering and adaptation, and use it for introgressing novel alleles into elite germplasm.