Citation: Badmus, U.O.; Crestani, G.; Cunningham, N.; Havaux, M.; Urban, O.; Jansen, M.A.K. UV Radiation Induces Specific Changes in the Carotenoid Profile of Arabidopsis thaliana. Biomolecules 2022, 12, 1879. https://doi.org/10.3390/ biom12121879 Academic Editors: Georgia Ntatsi, Vasileios Fotopoulos and Ivan Paponov Received: 22 November 2022 Accepted: 12 December 2022 Published: 14 December 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). biomolecules Article UV Radiation Induces Specific Changes in the Carotenoid Profile of Arabidopsis thaliana Uthman O. Badmus 1 , Gaia Crestani 1 , Natalie Cunningham 1 , Michel Havaux 2 , Otmar Urban 3 and Marcel A. K. Jansen 1,3, * 1 School of Biological, Earth and Environmental Sciences & Environmental Research Institute, University College Cork, Distillery Fields, North Mall, T23 N73K Cork, Ireland 2 Bioscience and Biotechnology Institute of Aix-Marseille, Aix-Marseille University, CEA, CNRS, UMR7265, CEA/Cadarache, F-13115 Saint-Paul-lez-Durance, France 3 Laboratory of Ecological Plant Physiology, Global Change Research Institute, Czech Academy of Sciences, Brno, Belidla 4a, CZ-60300 Brno, Czech Republic * Correspondence: m.jansen@ucc.ie Abstract: UV-B and UV-A radiation are natural components of solar radiation that can cause plant stress, as well as induce a range of acclimatory responses mediated by photoreceptors. UV-mediated accumulation of flavonoids and glucosinolates is well documented, but much less is known about UV effects on carotenoid content. Carotenoids are involved in a range of plant physiological processes, including photoprotection of the photosynthetic machinery. UV-induced changes in carotenoid profile were quantified in plants (Arabidopsis thaliana) exposed for up to ten days to supplemental UV radiation under growth chamber conditions. UV induces specific changes in carotenoid profile, including increases in antheraxanthin, neoxanthin, violaxanthin and lutein contents in leaves. The extent of induction was dependent on exposure duration. No individual UV-B (UVR8) or UV-A (Cryptochrome or Phototropin) photoreceptor was found to mediate this induction. Remarkably, UV-induced accumulation of violaxanthin could not be linked to protection of the photosynthetic machinery from UV damage, questioning the functional relevance of this UV response. Here, it is argued that plants exploit UV radiation as a proxy for other stressors. Thus, it is speculated that the function of UV-induced alterations in carotenoid profile is not UV protection, but rather protection against other environmental stressors such as high intensity visible light that will normally accompany UV radiation. Keywords: carotenoid; xanthophyll; photoreceptor; photosynthesis; arabidopsis; UV-B 1. Introduction In the natural environment plants are subjected to a complex spectrum of light that includes, amongst others, ultraviolet (UV; 280–400 nm), visible (400–700 nm), and far-red (FR; 700–780 nm) wavelengths. The quality and quantity of light are crucial in controlling plant growth and development [1,2]. UV-B (280–315 nm) is an integral part of the solar spectrum, although in the natural environment wavelengths shorter than 290 nm are not normally detectable. UV-B is considered a regulator and/or stressor depending on the intensity [3]. As a regulator, UV-B triggers multiple protective responses in plants such as the induction of antioxidant defences and photorepair capacity, accumulation of a broad range of metabolites and changes to plant morphology [4–7]. Conversely, as a stressor, UV-B exposure can reduce photosynthetic efficiency, and cause Reactive Oxygen Species (ROS) production and DNA damage [8–10]. UV-A radiation (315–340 nm) is less reactive on a per photon basis but can also cause both inhibitory and stimulatory effects on plants [11]. There is a wealth of knowledge on the relationship between UV-exposure and metabo- lite accumulation in plants. Reports have been published on the UV-induced accumu- lation of metabolites such as flavonoids, glucosinolates, anthocyanins, tocopherols, and Biomolecules 2022, 12, 1879. https://doi.org/10.3390/biom12121879 https://www.mdpi.com/journal/biomolecules