UV-B photoreceptor-mediated signalling in plants

doi:10.1016/j.tplants.2012.01.007

Trends in Plant Science

Volume 17, Issue 4, April 2012, Pages 230-237

https://doi.org/10.1016/j.tplants.2012.01.007 Get rights and content

Ultraviolet-B radiation (UV-B) is a key environmental signal that is specifically perceived by plants to promote UV acclimation and survival in sunlight. Whereas the plant photoreceptors for visible light are rather well characterised, the UV-B photoreceptor UVR8 was only recently described at the molecular level. Here, we review the current understanding of the UVR8 photoreceptor-mediated pathway in the context of UV-B perception mechanism, early signalling components and physiological responses. We further outline the commonalities in UV-B and visible light signalling as well as highlight differences between these pathways.

Section snippets

Plants and their light environment

Plants are sessile photoautotrophic organisms and thus must constantly adapt to surrounding environmental factors for optimal growth and development. Light in particular is an environmental factor of utmost importance to plants. It is not only the source of energy, driving photosynthesis, but also an informational signal directing plant development from germination to flowering. Plants sense the quality (wavelength), intensity, duration (including day length) and direction of light, and these

UV-B perception by the UVR8 photoreceptor

UVR8 is a β-propeller protein originally identified in a screen for Arabidopsis mutants hypersensitive to UV-B [13]. Under light conditions that specifically activate the UV-B photoreceptor pathway, UVR8 proteins are absolutely required for UV-B responses [14]. By contrast, at increased UV-B levels UV-B stress responses are maintained in the uvr8 mutant [15].

The UVR8 protein is localised in the cytoplasm and the nucleus and its abundance is unaffected by UV-B or other light qualities 14, 16.

UVR8-mediated signal transduction

UVR8 must be associated with a molecular signalling pathway for UV-B perception to be translated into plant photomorphogenesis and UV-B acclimation. However, only few of the molecular players involved in UVR8-mediated UV-B signal transduction are currently known. Regardless, there is solid evidence that COP1 and HY5, two common elements in light signalling, both play major roles in promoting UV-B-induced photomorphogenesis (Figure 3).

Negative feedback regulation of the UVR8 signalling pathway

The enhanced UV-B photomorphogenic response in transgenic UVR8 overexpression lines is associated with dwarf growth, highlighting the importance of achieving balance between UV-B-specific responses and plant growth [14]. A negative feedback regulation of UVR8 signalling by the UVR8-interacting REPRESSOR OF UV-B PHOTOMORPHOGENESIS1 (RUP1) and RUP2 proteins has recently been described [43]. RUP1 and RUP2 were identified and described in parallel as EARLY FLOWERING BY OVEREXPRESSION 1 (EFO1) and

UVR8-mediated UV-B responses

The identification of UVR8 as the UV-B photoreceptor now allows investigation of UVR8 involvement in known UV-B responses, as already shown for gene expression, UV-B acclimation and tolerance, and hypocotyl growth inhibition 13, 14, 17. Involvement of UVR8 in the control of endoreduplication and leaf morphogenesis, including stomatal differentiation, has also been proposed [48]. HY5 was recently implicated in UV-B-mediated cotyledon expansion [49], suggesting that UVR8 also plays a role in this

Commonalities with and differences to visible light signalling

In common with some of the other plant photoreceptors (in response to their respective wavebands), UVR8 accumulates rapidly in the nucleus in response to UV-B, requires UV-B to be activated (e.g. nuclear localization is not sufficient for UV-B signalling), interacts directly with COP1, uses HY5 as a downstream effector and is regulated by a negative feedback pathway. The fact that COP1 and HY5 are major downstream effectors in UV-B as well as in visible light signalling indicates high potential

Concluding remarks and future outlook

Significant progress has been made over recent years in identifying the molecular players and understanding the early mechanisms and functions of the UV-B perception and signalling pathway in plants. The perception of UV-B by UVR8 followed by UVR8–COP1 interaction has emerged as a primary mechanism of the UV-B response that is crucial for UV-B acclimation and tolerance. However, several open questions remain regarding the photochemistry, signal transduction and regulatory mechanisms of UVR8

Acknowledgements

We would like to thank Marina Gonzàlez Besteiro, Kimberley Tilbrook and Pat King for helpful comments on the manuscript. Research in the Ulm laboratory is supported by the University of Geneva, the Emmy Noether Programme (Grant UL341/1-1) and the Swiss National Science Foundation (Grant no. 31003A_132902).

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Trends in Plant Science

ReviewUV-B photoreceptor-mediated signalling in plants

Section snippets

Plants and their light environment

UV-B perception by the UVR8 photoreceptor

UVR8-mediated signal transduction

Negative feedback regulation of the UVR8 signalling pathway

UVR8-mediated UV-B responses

Commonalities with and differences to visible light signalling

Concluding remarks and future outlook

Acknowledgements

Trends Ecol. Evol.

Trends Ecol. Evol.

Curr. Top. Dev. Biol.

Trends Plant Sci.

Curr. Opin. Plant Biol.

Plant Sci.

Mol. Plant

Trends Cell Biol.

Curr. Biol.

J. Biol. Chem.

Plant Physiol. Biochem.

Mol. Plant

Curr. Biol.

Changes in biologically active ultraviolet radiation reaching the Earth's surface

Photochem. Photobiol. Sci.

Perception of UV-B by the Arabidopsis UVR8 protein

Science

Effects of solar ultraviolet radiation on terrestrial ecosystems. Patterns, mechanisms, and interactions with climate change

Photochem. Photobiol. Sci.

Repair of DNA damage induced by solar UV

Photosynth. Res.

Signal transduction in responses to UV-B radiation

Annu. Rev. Plant Biol.

Arabidopsis UVR8 regulates ultraviolet-B signal transduction and tolerance and contains sequence similarity to human regulator of chromatin condensation 1

Plant Physiol.

Interaction of COP1 and UVR8 regulates UV-B-induced photomorphogenesis and stress acclimation in Arabidopsis

EMBO J.

Arabidopsis MAP kinase phosphatase 1 and its target MAP kinases 3 and 6 antagonistically determine UV-B stress tolerance, independent of the UVR8 photoreceptor pathway

Plant J.

UV-B promotes rapid nuclear translocation of the Arabidopsis UV-B specific signaling component UVR8 and activates its function in the nucleus

Plant Cell

A UV-B-specific signaling component orchestrates plant UV protection

Proc. Natl. Acad. Sci. U.S.A.

CONSTITUTIVELY PHOTOMORPHOGENIC1 is required for the UV-B response in Arabidopsis

Plant Cell

FHY1 and FHL act together to mediate nuclear accumulation of the phytochrome A photoreceptor

Plant Cell Physiol.

Photoexcited CRY2 interacts with CIB1 to regulate transcription and floral initiation in Arabidopsis

Science

Blue-light-dependent interaction of cryptochrome 1 with SPA1 defines a dynamic signaling mechanism

Genes Dev.

Arabidopsis cryptochrome 1 interacts with SPA1 to suppress COP1 activity in response to blue light

Genes Dev.

A light-switchable gene promoter system

Nat. Biotechnol.

The third chromophore of DNA photolyase: Trp-277 of Escherichia coli DNA photolyase repairs thymine dimers by direct electron transfer

Proc. Natl. Acad. Sci. U.S.A.

Lightening up the UV response by identification of the arylhydrocarbon receptor as a cytoplasmatic target for ultraviolet B radiation

Proc. Natl. Acad. Sci. U.S.A.

Is the photoactive yellow protein a UV-B/blue light photoreceptor?

Photochem. Photobiol. Sci.

Review
UV-B photoreceptor-mediated signalling in plants