Molecular bases of signaling processes regulated by cryptochrome sensory photoreceptors in plants

Abstract

The blue-light sensors cryptochromes compose the widespread class of flavoprotein photoreceptors, regulating in plants signaling processes underlying their development, growth, and metabolism. In several algae cryptochromes may act not only as sensory photoreceptors but also as photolyases, catalyzing the repair of UV-induced DNA lesions. Cryptochromes bind FAD as the chromophore in the photolyase homologous region (PHR) domain and contain the cryptochrome C-terminal extension (CCE), which lacks in photolyases. Photosensory process in cryptochrome is initiated by photochemical chromophore conversions, including the formation of FAD redox forms. In a state with the chromophore reduced to neutral radical (FADH•), photoreceptory protein undergoes phosphorylation, conformational changes, and disengagement of the PHR domain and CCE with the subsequent formation of oligomers of cryptochrome molecules. Photooligomerization is a structural basis of functional activity of cryptochromes, which determines the formation of their complexes with variety of signaling proteins, including transcriptional factors and transcription regulators. Interactions in such complexes change the protein signaling activity, leading to gene expression regulation and plant photomorphogenesis. In recent years, multiple papers, reporting novel, more detailed information about molecular mechanisms of above-mentioned processes were published. The present review largely focuses on the analysis of data contained in these publications, particularly regarding structural aspects of cryptochrome transitions into photoactivated states and regulatory signaling processes mediated by cryptochrome photoreceptors in plants.