Citation: Tapia, G.; Castro, M.; Gaete-Eastman, C.; Figueroa, C.R. Regulation of Anthocyanin Biosynthesis by Drought and UV-B Radiation in Wild Tomato (Solanum peruvianum) Fruit. Antioxidants 2022, 11, 1639. https://doi.org/10.3390/ antiox11091639 Academic Editors: Agustín G. Asuero and Noelia Tena Received: 20 July 2022 Accepted: 21 August 2022 Published: 24 August 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/). antioxidants Article Regulation of Anthocyanin Biosynthesis by Drought and UV-B Radiation in Wild Tomato (Solanum peruvianum) Fruit Gerardo Tapia 1, * , Monserrat Castro 2 , Carlos Gaete-Eastman 3 and Carlos R. Figueroa 4,5, * 1 Unidad de Recursos Genéticos, Instituto de Investigaciones Agropecuarias, INIA Quilamapu, Chillán 3800062, Chile 2 Faculty of Forest Sciences, Universidad de Concepción, Concepción 4070386, Chile 3 Institute of Biological Sciences, Universidad de Talca, Talca 3465548, Chile 4 Laboratory of Plant Molecular Physiology, Institute of Biological Sciences, Universidad de Talca, Talca 3465548, Chile 5 Millennium Nucleus for the Development of Super Adaptable Plants (MN-SAP), Santiago 8340755, Chile * Correspondence: gtapia@inia.cl (G.T.); cfigueroa@utalca.cl (C.R.F.); Tel.: +56-42-2206743 (G.T.); +56-71-2200276 (C.R.F.) Abstract: Anthocyanins are plant pigments derived from the phenylpropanoid pathway which are produced in many different species, contributing to defense against stresses by their antioxidant properties. Cultivated tomatoes cannot synthesize flavonoids; however, wild tomatoes such as Solanum chilense and Solanum lycopersicoides have anthocyanin pigmented skin. Other wild tomato species such as Solanum peruvianum have been poorly studied concerning anthocyanin accumulation in the fruit. This research is the first to address the regulation of anthocyanin biosynthesis mediated by drought stress and light radiation in S. peruvianum fruit. Transcript accumulation of SpAN2, encoding for a key MYB type transcription factor for the regulation of anthocyanin biosynthesis, was induced in the fruit of plants exposed to drought treatment. In addition, fruit peel accumulates a greater anthocyanin content in water deficit-treated plants. The expression of SpAN2 was also regulated according to sunlight exposure, reaching a higher expression during maximal daily UV radiation and under controlled UV-B treatments. Similar results were observed for the expression of the late flavonoid biosynthetic gene dihydroflavonol 4-reductase (SpDFR). These results suggest that SpAN2 and SpDFR are involved in anthocyanin biosynthesis under drought stress and UV radiation in S. peruvianum. Keywords: anthocyanin; drought stress; R2R3 MYB transcription factor; Solanum peruvianum; UV radiation; wild tomato 1. Introduction Anthocyanins are an important class of flavonoids that represent a large group of plant secondary metabolites. Anthocyanins are glycosylated polyphenolic compounds with a range of colors varying from orange, red, and purple to blue in flowers, seeds, fruits, and vegetative tissues [1]. Anthocyanins protect plants against various biotic and abiotic stresses like drought and UV radiation [2,3], partially due to their powerful antioxidant properties. In addition, anthocyanin-rich food products have become increasingly popular due to their attractive colors and suggested benefits for human health [4,5]. Most higher plants can synthesize anthocyanins, but the exact nature of the antho- cyanins formed can differ widely in plant species due to the activity of specific enzymes that add sugars, methyl groups, and acyl residues to the basic anthocyanidin structure [6]. An- thocyanin biosynthesis is generally catalyzed by a total of nine conserved enzymes: pheny- lalanine ammonium-lyase (PAL), cinnamate 4-hydroxylase (C4H), p-coumaroyl 4-CoA ligase (4CL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR) and anthocyanidin synthase (ANS). The DFR Antioxidants 2022, 11, 1639. https://doi.org/10.3390/antiox11091639 https://www.mdpi.com/journal/antioxidants