Regulation of flowering time by light

Abstract

To predict the arrival of the favorable season, plants monitor environmental variables such as light and temperature. Light is perceived by several families of photoreceptors, the phytochromes, the cryptochromes and the LOV domain containing photoreceptors. The photoreceptors have an important role in entraining the circadian clock, which regulates the phase of expression of flowering time genes, like CONSTANS (CO). As a central component of the photoperiod pathway, CO is transcriptionally regulated by a second layer of regulators, which comprise LOV photoreceptors, GIGANTEA and the CDF transcription factors. To ensure flowering is promoted by longdays, phytochrome B promotes CO protein turnover early in the morning whereas cryptochromes and phytochrome A promote CO stability later on, when the CO mRNA expression peak coincides with the light phase of long-days. The small family of SPA proteins and COP1 are involved in CO degradation, a pathway that is prevented by blue-light in a cryptochrome dependent manner. Flowering is also regulated by changes in light quality and other CO-independent mechanisms, but light responses converge on the expression of two small proteins, FT and its homolog TSF, which are able to move to the apical meristem and interact with transcription factors to promote reproductive development.