Fungi Journal of Article Sterol Composition Modulates the Response of Saccharomyces cerevisiae to Iron Deficiency Tania Jordá 1 , Nicolas Rozès 2 and Sergi Puig 1, *   Citation: Jordá, T.; Rozès, N.; Puig, S. Sterol Composition Modulates the Response of Saccharomyces cerevisiae to Iron Deficiency. J. Fungi 2021, 7, 901. https://doi.org/10.3390/jof7110901 Academic Editor: Ivan-Kresimir Svetec Received: 17 September 2021 Accepted: 22 October 2021 Published: 25 October 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 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/). 1 Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de Alimentos (IATA), Consejo Superior de Investigaciones Científicas (CSIC), 46980 Valencia, Spain; tajorsan@iata.csic.es 2 Departament de Bioquímica i Biotecnología, Facultat d’Enologia, Universitat Rovira i Virgili, 43007 Tarragona, Spain; nicolasrozes@urv.cat * Correspondence: spuig@iata.csic.es Abstract: Iron is a vital micronutrient that functions as an essential cofactor in multiple biological processes, including oxygen transport, cellular respiration, and metabolic pathways, such as sterol biosynthesis. However, its low bioavailability at physiological pH frequently leads to nutritional iron deficiency. The yeast Saccharomyces cerevisiae is extensively used to study iron and lipid metabolisms, as well as in multiple biotechnological applications. Despite iron being indispensable for yeast ergosterol biosynthesis and growth, little is known about their interconnections. Here, we used lipid composition analyses to determine that changes in the pattern of sterols impair the response to iron deprivation of yeast cells. Yeast mutants defective in ergosterol biosynthesis display defects in the transcriptional activation of the iron-acquisition machinery and growth defects in iron-depleted conditions. The transcriptional activation function of the iron-sensing Aft1 factor is interrupted due to its mislocalization to the vacuole. These data uncover novel links between iron and sterol metabolisms that need to be considered when producing yeast-derived foods or when treating fungal infections with drugs that target the ergosterol biosynthesis pathway. Keywords: baker’s yeast; Saccharomyces cerevisiae; iron deficiency; sterols; ergosterol; Upc2; Ecm22; Aft1 1. Introduction Iron is an indispensable element for the large majority of living organisms because it functions as an essential cofactor in oxygen transport, respiration, and many metabolic processes, including lipid biosynthesis. Despite the iron abundance, the low solubility of its oxidized form (Fe 3+ ) at physiological pH dramatically limits iron bioavailability. Thus, iron deficiency is a widely extended nutritional disorder affecting humans (predominantly children and women), animals, and crops [1,2]. Strategies to prevent and treat human iron deficiency include diet diversification, iron supplementation, and fortification of food with iron [3]. Saccharomyces cerevisiae is one of the most important microorganisms in biotech- nology because it has been used since ancient times to obtain fermented foods (e.g., wine, beer, and bread) and, more recently, as a cell factory. Yeast itself is also consumed as a food supplement because it is especially rich in vitamins, proteins, and fiber. Importantly, iron-enriched yeasts can also be used to prevent and ameliorate iron deficiency symptoms in animals and humans [4–6]. Baker’s yeast is a reliable model organism to investigate the response of eukaryotes to iron limitation [7,8]. The response of S. cerevisiae to iron deficiency depends on the two partially overlapping Aft1 and Aft2 transcription factors. Upon iron deficit, these iron-sensing proteins accumulate in the nucleus, where they associate to iron-responsive promoter elements (FeRE) and promote the transcription of a set of genes known as the iron regulon, which includes the high-affinity iron acquisition complex FET3/FTR1, the iron-siderophore transporter ARN2, and the metalloreductase FRE4, whose main function J. Fungi 2021, 7, 901. https://doi.org/10.3390/jof7110901 https://www.mdpi.com/journal/jof