flowering

Light has a strong effect on the stability of proteins that regulate many physiological and developmental processes in animals and plants alike. Circadian rhythms depend on rapid accumulation and degradation of protein products within a 24-hour time window. Light to plants is more than a source of energy to generate sugars; it is an external timing apparatus (for most plants) that allows for the plant to reproduce when environmental conditions are favorable for offspring development. For floral initiation in Arabidopsis to take place, 16 hours of light per 24-hour period, is preferred. Light strikes the photoreceptors, PHYA, PHYB, and CRY2, which then entrain the circadian clock to trigger the expression of CONSTANS (CO). CO is a transcriptional regulator that is expressed (under appropriate conditions) in the leaf vasculature in most long day (16 hours of light, 8 hours of darkness).  CO expression follows an oscillatory trend throughout a 24-hour period, as the protein accumulates in light and is rapidly degraded in the dark. With the help of the transcriptional regulators that the Holt Lab studies (NF-Y), CO can bind to the promoter of a gene called FLOWERING LOCUS-T (FT). FT acts as the central hub for many flowering pathways. After FT has been activated, the protein product (produced in the leaves) travels against a natural gradient, through the phloem companion cells, where it eventually reaches the shoot apical meristem to turn on another group of transcription factors that induce flowering.