Plants rely on photoreceptors, including red/far-red light receptors phytochromes and blue/UV-A light receptors cryptochromes to regulate growth and development, including seed germination, de-etiolation, vegetative growth, and time to flower. Cryptochromes are flavoproteins that share sequence similarities to DNA photolyase (a blue light-dependent DNA repairing enzyme) but show no detectable photolyase activity. Since its first discovery in Arabidopsis, cryptochromes have been found to exist in a wide range of organisms from bacteria to human. Cryptochromes have been demonstrated to regulate the circadian clock in both plants and animals.
Arabidopsis has two cryptochromes, cry1 and cry2, which are nuclear proteins that mediate blue light control of cell elongation and photoperiodic induction of flowering, respectively.
The molecular mechanisms of Arabidopsis cryptochromes are not very clear. Blue light affects the expression of as much as 20% of the genes in the Arabidopsis genome, and cry1 and cry2 are the major photoreceptors mediating the blue light regulation of gene expression, which leads to a hypothesis that cryptochromes regulate plant growth and development via the control of gene expression. The question of how cryptochromes regulate gene expression changes in response to blue light is currently a major focus of our research. We have previously demonstrated that cry2 is a major photoreceptor regulating photoperiodic flowering, that cryptochromes and phytochromes act in three genetic pathways in response to different wavelength of light to regulate floral initiation, and that blue light-dependent cryptochrome phosphorylation is an important reaction associated with cryptochrome function and regulation. We are currently using various approaches, including molecular genetics, biochemistry, and genomics, to further investigate how cryptochromes act in the cell.