Abstract
The photoreceptors UV RESISTANCE LOCUS 8 (UVR8) and CRYPTOCHROMES 1 and 2 (CRYs) play major roles in the perception of UV-B (280-315 nm) and UV-A/blue radiation (315-500 nm), respectively. However, it is poorly understood how they function in sunlight. The roles of UVR8 and CRYs were assessed in a factorial experiment with Arabidopsis thaliana wild-type and photoreceptor mutants exposed to sunlight for 6 or 12 hr under five types of filters with cut-offs in UV and blue-light regions. Transcriptome-wide responses triggered by UV-B and UV-A wavelengths shorter than 350 nm (UV-Asw ) required UVR8 whereas those induced by blue and UV-A wavelengths longer than 350 nm (UV-Alw ) required CRYs. UVR8 modulated gene expression in response to blue light while lack of CRYs drastically enhanced gene expression in response to UV-B and UV-Asw . These results agree with our estimates of photons absorbed by these photoreceptors in sunlight and with in vitro monomerization of UVR8 by wavelengths up to 335 nm. Motif enrichment analysis predicted complex signaling downstream of UVR8 and CRYs. Our results highlight that it is important to use UV waveband definitions specific to plants' photomorphogenesis as is routinely done in the visible region.
Highlights
Sunlight regulates plant growth, development and acclimation to the environment, while responses to specific wavelengths are regulated by different photoreceptors
We tested four hypotheses: (a) the perception of solar UV-B and UV-A wavelengths up to 350 nm (UV-Asw) is through UV RESISTANCE LOCUS 8 (UVR8), (b) the perception of solar UV-A wavelengths above 350 nm (UV-Alw) and blue light is through CRYPTOCHROMES and 2 (CRYs), (c) crosstalk exists between UV-B/UV-Asw and UV-Alw/blue light signaling in plants exposed to sunlight and (d) gene expression responses to different wavelengths of sunlight are coordinated by multiple transcription factors (TFs) resulting in multiple patterns of expression
We found that UVR8 affected blue light-induced gene expression, as fewer and in part different genes responded to blue light in uvr8-2 when compared to Landsberg erecta (Ler) (Figures 2a,b, S5)
Summary
Development and acclimation to the environment, while responses to specific wavelengths are regulated by different photoreceptors. Plants are often grown under low and constant irradiance of white light (3.6–100 μmol m−2 s−1) and exposed to monochromatic UV-B, UV-A or blue radiation (Brown et al, 2005; Brown et al, 2009; Brown & Jenkins, 2008; Favory et al, 2009; Kleine et al, 2007; Ohgishi et al, 2004) These light conditions are different from the natural light environment where irradiance varies from day to day, and through each day. Results from an indoor experiment suggested the participation of UVR8 in flavonoid accumulation in response to UV-A from light-emitting diodes (LEDs) (Brelsford et al, 2018) It is not yet clear which UV-A wavelengths are perceived through UVR8 and which ones through CRYs. To assess the roles of UVR8 and CRYs in the perception of solar UV-B, UV-A and blue radiation, we measured transcriptome-wide. We tested four hypotheses: (a) the perception of solar UV-B and UV-A wavelengths up to 350 nm (UV-Asw) is through UVR8, (b) the perception of solar UV-A wavelengths above 350 nm (UV-Alw) and blue light is through CRYs, (c) crosstalk exists between UV-B/UV-Asw and UV-Alw/blue light signaling in plants exposed to sunlight and (d) gene expression responses to different wavelengths of sunlight are coordinated by multiple TFs resulting in multiple patterns of expression
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