Cryptochromes integrate green light signals into the circadian system

Abstract

Plants are acutely sensitive of their light environment, adapting their growth habit and prioritizing developmental decisions to maximize fecundity. In addition to providing an energy source and directional information, light quality also contributes to entrainment of the circadian system, an endogenous timing mechanism that integrates endogenous and environmental signalling cues to promote growth. Whereas plants' perception of red and blue portions of the spectrum are well defined, green light sensitivity remains enigmatic. In this study, we show that low fluence rates of green light are sufficient to entrain and maintain circadian rhythms in Arabidopsis and that cryptochromes contribute to this response. Importantly, green light responses are distinguishable from low blue light‐induced phenotypes. These data suggest a distinct signalling mechanism enables entrainment of the circadian system in green light‐enriched environments, such as those found in undergrowth and in densely planted monoculture.

Shades of green: untying the knots of green photoperception

“…Although a specific green photoreceptor has yet to be identified (see above), many of the green light-induced phenotypes observed are modulated by the manipulation of canonical photoreceptors. Plants are less responsive to green light than to other wavelengths within the photosynthetically active spectrum ( Folta and Maruhnich, 2007 ; Wang and Folta, 2013 ; Smith et al , 2017 ), with hypocotyl elongation only being modestly inhibited by increasing fluence rates of green light ( Ahmad et al , 2002 ; Battle and Jones, 2020 ). Green light is sufficient to induce seed germination in a phyA-dependent manner ( Shinomura et al , 1996 ), whereas overexpression of CRY1 induces green light hypersensitivity ( Lin et al , 1995 ; Bouly et al , 2007 ).…”

“…Green light is also sufficient to induce changes in gene expression (primarily repressing accumulation of plastid-encoded transcripts; Dhingra et al , 2006 ), while green light also maintains circadian rhythms in seedlings in a cryptochrome-independent manner. Despite this, cryptochromes regulate the pace of the circadian system under these conditions ( Battle and Jones, 2020 ). It consequently appears that green light is perceived by multiple, interconnected photoreceptor inputs to initiate a subset of photomorphogenic responses in response to illumination.…”

“…While cry1cry2 seedlings have low-amplitude rhythms under blue light, irradiation with green and blue light increases circadian amplitude in these lines while revealing an extended circadian free-running period. These observations suggest that either the cryptochromes play a role in circadian responses to green light distinct from those to blue light, or that additional photoreceptors, such as the phytochromes, operate in conjunction with the cryptochromes to regulate the circadian perception of green light ( Battle and Jones, 2020 ).…”

“…For instance, yellow light inhibits FLOWERING LOCUS T expression and cry2 degradation in response to blue light illumination ( Banerjee et al , 2007 ), leading to the inhibition of blue light-induced flowering ( Zhang et al , 2011 ; Wang and Folta, 2013 ). The disparity between the consequences of short- and long-wavelength green light irradiation suggests the involvement of additional photoreceptors (or light-activated pathways) in the modulation of a green light signal absorbed by the light-irradiated cryptochrome FADH· chromophore ( Table 1 ; Bouly et al , 2007 ; Battle and Jones, 2020 ). In this regard it is notable that phytochromes absorb yellow photons in preference to green light ( Fig.…”

Reproducing Solar Spectral Irradiance by LEDs

“…A recent study on the in uence of green light [22] emphasizes the potential of LED technology for photobiological research. It shows that low irradiance doses of green light are su cient to induce and maintain the circadian rhythms in thale cress (Arabidopsisthaliana) and that cryptochromes contribute to this reaction.…”