CORDIS - EU research results

Floral Integrating Networks at the Shoot Apical Meristem of Rice

Final Report Summary - FLARE (Floral Integrating Networks at the Shoot Apical Meristem of Rice)

Many plant species have evolved to measure and respond to changes in day length (or photoperiod), to align specific phases of the life cycle with external conditions. Flowering is a prominent example of a process controlled by day length and plant species can be categorized as long day plants (LDP), short day plants (SDP) or day neutral plants (DNP) based on the photoperiod most effective at inducing flower formation. Cultivated rice (Oryza sativa) is a short day plant of tropical origin that flowers as nights become longer. Upon perception of the correct photoperiod, leaves produce molecules called “florigens” that travel through the vascular tissue into the apex of the plant, where flowers are eventually formed.
Latitudinal adaptation of rice varieties has required the modification of photoperiod sensitivity, and varieties adapted to higher latitudes are almost insensitive to day length and can flower regardless of this input. The molecular mechanisms that have contributed to such expansion remain largely unknown. This project aimed at dissecting the regulatory networks that are necessary in the leaves to produce florigenic proteins at the correct time of the year, and in the apex to respond to such protein signals.
Studying the shoot apex, we have identified a regulatory gene specifically present in this tissue and turned off by arrival of a rice florigen. The gene is required to coordinate inflorescence formation and stem elongation, ensuring that they occur synchronously. Uncoupling these processes in plants that lack the gene function results in poor reproductive performances. The gene controls the metabolism of gibberellins, a plant hormone necessary for stem elongation, and our data indicate how florigens coordinate and integrate distinct molecular and hormonal signals, not directly related to flower production.
Regulatory networks in leaves have evolved to measure day length and we took advantage of varieties in which the measuring mechanism is compromised by mutations in specific genes. We first described such mutations in a panel of cultivated varieties, and suggested that they have been instrumental to expand rice to temperate environments in Europe. We further isolated novel mutations and determined the molecular mechanisms through which they affect the timing of flowering. We have developed a simple model that accounts for their activity. This molecular understanding of the system has applied value for breeding novel varieties. Using such understanding, we have bred some novel rice cultivars adapted to Mediterranean environments that are currently undergoing field trials.