Category: SenPEP activities

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How did we work out that UVR8 is a solar-UV-B plus UV-A photoreceptor?

What were our findings?

We reported in two recent research papers and an update review, that functional UVR8 is required for the perception by plants of solar UV-radiation with wavelengths shorter than approximately 340 nm, which includes the whole UV-B band plus the shorter wavelengths in the UV-A band. In sunlight, cryptochromes are required for the perception by plants of blue light and the longer wavelengths within the UV-A band leading to changes in gene expression. In sunlight cryptochrome-mediated signalling is driven mostly by violet and blue light with wavelength longer than 400 nm. In comparison wavelengths between 350 nm and 400 nm of solar radiation seem to play only a minor role in the regulation of gene expression.

This is an important step forward in our understanding of the perception of different wavelengths of sunlight by plants as the former accepted view was that UVR8 is a UV-B photoreceptor that participated only in the perception of UV-B radiation while all wavelengths of UV-A radiation were perceived by cryptochromes and the other UV-A/Blue photoreceptors, phototropins and ZTL.

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Cryptochromes and stomatal opening

Our recent paper, included in Fang Wang’s thesis:

Fang Wang, T Matthew Robson, Jorge J Casal, Alexey Shapiguzov, Pedro J Aphalo (2020) Contributions of cryptochromes and phototropins to stomatal opening through the day. Functional Plant Biology, 47, 226-238. DOI: https://doi.org/10.1071/FP19053.

The role of phototropins in stomatal opening in response to blue light in well documented in the literature. Reports of a role for cryptochromes in this response have been few, and to some extent contradictory. Most studies on the daily patterns of stomatal opening date from the time when well described photoreceptor mutants were not yet available, so using these mutants was expected to reveal new features of stomatal responses.

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UVR8 is an UV-B and UV-A photoreceptor

Our two recent papers:

Neha Rai, Susanne Neugart, Yan Yan, Fang Wang, Sari M Siipola, Anders V Lindfors, Jana Barbro Winkler, Andreas Albert, Mikael Brosché, Tarja Lehto, Luis O Morales, Pedro J Aphalo (2019) How do cryptochromes and UVR8 interact in natural and simulated sunlight? Journal of Experimental Botany, 70, 4975–4990. https://doi.org/10.1093/jxb/erz236

Neha Rai, Andrew O’Hara, Daniel Farkas, Omid Safronov, Khuanpiroon Ratanasopa, Fang Wang, Anders V. Lindfors, Gareth I. Jenkins, Tarja Lehto, Jarkko Salojärvi, Mikael Brosché, Åke Strid, Pedro J. Aphalo, Luis O. Morales (2020) The photoreceptor UVR8 mediates the perception of both UV‐B and UV‐A wavelengths up to 350 nm of sunlight with responsivity moderated by cryptochromes. Plant, Cell & Environment, https://doi.org/10.1111/pce.13752

In these two recent publications we have shown that UVR8, previously described as an ultravioltet-B (UV-B, 280-315 nm) photoreceptor, in sunlight functions both as an ultraviolet-A (UV-A, 315-400 nm) and UV-B photoreceptor. Although UVR8 presents maximal absorption at the boundary between ultraviolet-C (UV-C, <280 nm) and UV-B, the shape of the solar spectrum in the ultraviolet region, characterized by a very steep slope, allows the UVR8 protein to absorb nearly as many UV-A photons as UV-B photons, and obviously no photons in the UV-C as they are not present in sunlight at ground level.

Normalized spectral absoorbance of UVR8 protein in vitro (From Rai et al.. 2020).

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Measuring campaign in the Alps

I joined a field measuring campaign organized by my collaborator T. Matthew Robson (see Matt’s CanSEE website for information on the research project) with the participation of José Ignacio García Plazaola and Beatriz Fernandez-Marin from the University of the Basque-Country.

Matthew described the aim of our work as:

By characterising the patterns of response to UV radiation in terms of the photoprotection and UV-screening of plants across a diversity of species, we hope to better understand how and why these response evolved and what environmental cues underpin their induction.

We spent the last weeks of May the at 2100 m a.s.l. in the Alps at the Jardin Botanique du Lautaret measuring solar radiation and the responses of plants to it. I did some measurements of solar radiation but spent most of the time photographing plants and lichens to record their optical properties in the ultraviolet-A, visible and near-infrared regions of the spectrum.

Villar-d’Arêne, French Alps, 2100 m a.s.l.

Several of the photographs I took of site, crew, plants and lichens available at my photography website in a post published earlier today (as I have the server set up for easy creation of galleries). These photographs are stored at Flickr.

Matthew has also written a post about the trip and project in his blog.

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Perspectives on plant UV-research and its applications

An article, titled “A perspective on ecologically relevant plant-UV research and its practical application”, to be included in the PPS special issue, has been published on-line. It originated on discussions at the second UV4Plants Network meeting held in Bled last year, but writing and editing continued for several months. The article has been published under open access and is available through PPS’ web site. Several members of our research group and some of our collaborators are co-authors.

The graphical and text abstracts are reproduced below.

Graphical abstract from the article. Copyrighted (c) 2019.

Abstract

Plants perceive ultraviolet-B (UV-B) radiation through the UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8), and initiate regulatory responses via associated signalling networks, gene expression and metabolic pathways. Various regulatory adaptations to UV-B radiation enable plants to harvest information about fluctuations in UV-B irradiance and spectral composition in natural environments, and to defend themselves against UV-B exposure. Given that UVR8 is present across plant organs and tissues, knowledge of the systemic signalling involved in its activation and function throughout the plant is important for understanding the context of specific responses. Fine-scale understanding of both UV-B irradiance and perception within tissues and cells requires improved application of knowledge about UV-attenuation in leaves and canopies, warranting greater consideration when designing experiments. In this context, reciprocal crosstalk among photoreceptor-induced pathways also needs to be considered, as this appears to produce particularly complex patterns of physiological and morphological response. Through crosstalk, plant responses to UV-B radiation go beyond simply UV-protection or amelioration of damage, but may give cross-protection over a suite of environmental stressors. Overall, there is emerging knowledge showing how information captured by UVR8 is used to regulate molecular and physiological processes, although understanding of upscaling to higher levels of organisation, i.e. organisms, canopies and communities remains poor. Achieving this will require further studies using model plant species beyond Arabidopsis, and that represent a broad range of functional types. More attention should also be given to plants in natural environments in all their complexity, as such studies are needed to acquire an improved understanding of the impact of climate change in the context of plant-UV responses. Furthermore, broadening the scope of experiments into the regulation of plant-UV responses will facilitate the application of UV radiation in commercial plant production. By considering the progress made in plant-UV research, this perspective highlights prescient topics in plant-UV photobiology where future research efforts can profitably be focussed. This perspective also emphasises burgeoning interdisciplinary links that will assist in understanding of UV-B effects across organisational scales and gaps in knowledge that need to be filled so as to achieve an integrated vision of plant responses to UV-radiation.