How Plants Know it's Time to Flower

Light-dependent formation of a protein complex allows plants to monitor seasonal changes in daylight so that they can, in effect, select the most favorable time for flowering, according to Takato Imaizumi and colleagues at Scripps Research Institute (Science, DOI: 10.1126/science.1146994). The researchers studied the effect in Arabidopsis, a small flowering plant related to mustard and cabbage. Focusing on the plant proteins FKF1 and GI, the researchers determined that FKF1 is a photoreceptor for blue light and forms a complex with GI when exposed to sunlight. Production of the two proteins in the plant varies throughout the day but peaks simultaneously only during days with enough hours of light. Under these conditions, sufficient quantities of the FKF1-GI complex are formed to destroy a third protein known as CDF1. Because CDF1 represses expression of a gene that triggers flowering, its destruction frees Arabidopsis to flower.