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).

The longer the wavelength the less energy photons carry, and this may limit their ability to drive photochemical reactions, such as the activation of a photoreceptor. We show that somewhere near 340 to 350 nm there is a transition, with photons at longer wavelengths, even if absorbed not leading to monomerization and activation of the UVR8 photoreceptor.

Plants have other photoreceptors capable of absorbing ultraviolet-A radiation: cryptochromes (cry1, cry2), phototropins (phot1, phot2) and proteins in the Zeitloup family (zl). In sunlight, cry1 and cry2 , are mainly activated by blue light (BL) and they seem to play a smaller direct role in the UV-A region of sunlight. However, the action of cry1 and/or cry2 very strongly down-regulates responses to UV-A and UV-B mediated by UVR8.

Finally we also showed that both the cry1 cry2 and uvr8-2 mutants survive and grow almost normally in full sunlight, while full sunlight  kills within a few days of germination most individuals of the cry1 cry uvr8-2 triple mutant.

Clockwise from top left: uvr8-2 cry1 cry2 mutant; uvr8-2 mutant; cry1 cry2 mutant; Ler wild type.

Take home message: UVR8 should be in the future described as a UV-B/UV-A photoreceptor. When studying plants, for measurements and treatments to be informative need to divide the UV-A range into two regions UV-Asw and UV-Alw with a split at 350 nm as we have used, or following CIEs definitions of UV-A1 and UV-A2 with a split at 340 nm. Fully understanding the mechanisms of perception of ultraviolet radiation by plants will require additional studies aiming at disentangling the many signalling interactions downstream of these and other photoreceptors.

How we did it: Pedro J. Aphalo and Luis O. Morales lead this research and generated the main hypotheses, but the success of these studies was made possible by intellectual and practical contributions from several other research groups from Finland, Sweden, Germany, Singapore and Great Britain. It took nearly six years since we started suspecting  that UVR8 played a role in UV-A perception in sunlight and the publication of these articles were we demonstrate why and how UVR8 functions as UV-B/UV-A photoreceptor in sunlight. Both the process and the achievement were highly rewarding intellectually in spite of the lack of enthusiasm shown by several grant-application reviewers along the way and the slow-down this caused.

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.

Researchers mentoring researchers

Mentoring has been an everyday activity for me as supervisor of students (PhD and MSc) and postdoctoral researchers. This mentoring has usually focused mainly on research itself, and the specific field of research I work in. In addition I have brought to the discussion more general topics but they had been mostly unplanned detours from other discussions. To some extent, answering questions in ResearchGate, StackOverflow and through e-mail, has also been small-scale mentoring. I have regularly taught at and organized training events for PhD students and early stage researchers. In recent years I have edited a handbook on methods in photobiology, and co-authored another one on calculations related to photobiology. I have written a text book on the R language, aimed mainly at independent learning. I have developed open-source software to make correct calculations and plotting of radiation data as used in photobiology easier. The aim behind all this work has been to make “good science” easier to carry out, and through mentoring and training, to encourage other researchers in my own field to pay more attention into avoiding methodological pitfalls. Continue reading “Researchers mentoring researchers”

Grant application

We have submitted a joint grant application to the Academy of Finland and National Science Foundation of China. Our Chinese partner is Prof. Hailiang Xu and his team, from the Chinese Academy of Science at Urumqi, Xinjiang in Western China. The proposal is related to the desert riparian forest along the river Tarim, and its dominant tree, Populus euphratica.

View Map

[cetsEmbedGmap src=https://maps.google.com/?ll=40.880295,81.474609&spn=26.384316,36.826172&t=h&z=5 width=350 height=425 marginwidth=0 marginheight=0 frameborder=0 scrolling=no]