Signaling mechanisms of plant cryptochromes in Arabidopsis thaliana

Abstract

Cryptochromes (CRY) are flavoproteins that direct a diverse array of developmental processes in response to blue light in plants. Conformational changes in CRY are induced by the absorption of photons and result in the propagation of light signals to downstream components. In Arabidopsis, CRY1 and CRY2 serve both distinct and partially overlapping functions in regulating photomorphogenic responses and photoperiodic flowering. For example, both CRY1 and CRY2 regulate the abundance of transcription factors by directly reversing the activity of E3 ubiquitin ligase on CONSTITUTIVE PHOTOMORPHOGENIC 1 and SUPPRESSOR OF PHYA-105 1 complexes in a blue light-dependent manner. CRY2 also specifically governs a photoperiodic flowering mechanism by directly interacting with a transcription factor called CRYPTOCHROMEINTERACTING BASIC-HELIX-LOOP-HELIX. Recently, structure/function analysis of CRY1 revealed that the CONSTITUTIVE PHOTOMORPHOGENIC 1 independent pathway is also involved in CRY1-mediated inhibition of hypocotyl elongation. CRY1 and CRY2 thus not only share a common pathway but also relay light signals through distinct pathways, which may lead to altered developmental programs in plants.

Coordination of Cryptochrome and Phytochrome Signals in the Regulation of Plant Light Responses

“…However, the largest difference in signal transduction mechanisms between cry1 and cry2 is that only cry2 can bind with CIBs, which are specialized to function in photoperiodic flowering, in a B light-dependent manner [84,85]. Namely, the COP1/SPA or the PIF pathway likely represents the overlapping functions between cry1 and cry2, and the CIB pathway may confer on cry2 its more specific roles in the regulation of photoperiodic flowering [106]. However, the mechanism by which the COP1/SPA pathway and CIB pathway, which both regulate FT expression, converge downstream of cry2 is still unknown.…”

Diverse photoreceptors and light responses in plants

“…Nagano (2016) reviewed molecular structures of prokaryotic and plant phytochromes and discussed their functional universality and diversity by the comparison of prokaryotic and eukaryotic phytochromes. Liu et al (2016) reviewed the molecular mechanisms underlying cry signaling in Arabidopsis that cover the photoreaction mechanisms of FAD (flavin-adenine-di-nucleotide) and the Trp-triad, phosphorylation of cry C-terminal extension and signaling complex with several signaling factors. They nicely summarized the differences in cry1 and cry2 signaling complexes and their signal cascades.…”

Optogenetics: A Primer for Chemists

“…In addition, small‐molecule metabolites (e.g., ATP, NADH) have been shown to augment non‐(Trp triad) electron‐transfer pathways . Cry photoactivation induces a conformational change that promotes a binding interaction with various protein partners, including the cryptochrome‐interacting basic‐helix–loop–helix protein (CIB) . A 170‐residue fragment of the latter has been used, in combination with Cry‐modified proteins, to control the intracellular location of proteins of interest in a light‐triggered fashion .…”