Abstract

Plants display a remarkable degree of plasticity, altering their growth and development in response to an array of environmental cues. We use domesticated sunflower as a model to investigate how this plasticity is modified by the circadian system. Domesticated sunflower is well-known for its heliotropic behavior, with stems bending to follow the sun from east to west during the day and then bending from west to east during the night so they face east before the sun rises in the morning. Sunflowers are also famous for the remarkable spiral arrangement of florets on their composite inflorescences, a pattern imposed early in development. It is less recognized that during late-stage floral development this spiral pattern is transformed into one of concentric rings. We find that both solar tracking of stems and spatial patterns seen in late-stage floral development are generated by interactions between the circadian system and environmental signaling pathways and demonstrate the importance of this coordination for plant reproductive fitness.