Fungi Journal of Article Osmolyte Signatures for the Protection of Aspergillus sydowii Cells under Halophilic Conditions and Osmotic Shock Eya Caridad Rodríguez-Pupo 1,2,† , Yordanis Pérez-Llano 1,2,† , José Raunel Tinoco-Valencia 3 , Norma Silvia Sánchez 4 , Francisco Padilla-Garfias 4 , Martha Calahorra 4 , Nilda del C. Sánchez 5 , AyixónSánchez-Reyes 6 , María del Rocío Rodríguez-Hernández 1 , Antonio Peña 4 , Olivia Sánchez 4 , Jesús Aguirre 4 , Ramón Alberto Batista-García 2 , Jorge Luis Folch-Mallol 1 and María del Rayo Sánchez-Carbente 1, *   Citation: Rodríguez-Pupo, E.C.; Pérez-Llano, Y.; Tinoco-Valencia, J.R.; Sánchez, N.S.; Padilla-Garfias, F.; Calahorra, M.; Sánchez, N.d.C.; Sánchez-Reyes, A.; Rodríguez-Hernández, M.d.R.; Peña, A.; et al. Osmolyte Signatures for the Protection of Aspergillus sydowii Cells under Halophilic Conditions and Osmotic Shock. J. Fungi 2021, 7, 414. https://doi.org/10.3390/jof7060414 Academic Editor: Francesca Scandellari Received: 18 April 2021 Accepted: 20 May 2021 Published: 26 May 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 Centro de Investigación en Biotecnología, Universidad Autónoma del Estado de Morelos (UAEM), Av. Universidad 1001, Col. Chamilpa, Cuernavaca C.P. 62209,Morelos, Mexico; eyarguez2013@gmail.com (E.C.R.-P.); yordanis.perezllano@yahoo.com (Y.P.-L.); rocio.rodriguez@uaem.mx (M.d.R.R.-H.); jordi@uaem.mx (J.L.F.-M.) 2 Centro de Investigación en Dinámica Celular, IICBA, UAEM, Av. Universidad 1001, Col. Chamilpa, Cuernavaca C.P. 62209, Morelos, Mexico; rabg@uaem.mx 3 Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Campus Morelos, Av. Universidad 1001, Col. Chamilpa, Cuernavaca C.P. 62210,Morelos, Mexico; raunel@ibt.unam.mx 4 Instituto de Fisiología Celular, UNAM, Cto. Exterior s/n, Cd. Universitaria, Coyoacán, Ciudad de México C.P. 04510, Federal District, Mexico; nsanchez@ifc.unam.mx (N.S.S.); fpadilla@ifc.unam.mx (F.P.-G.); mcalahor@ifc.unam.mx (M.C.); apd@ifc.unam.mx (A.P.); asanchez@ifc.unam.mx (O.S.); jaguirre@ifc.unam.mx (J.A.) 5 Centro de Ciencias Genómicas, UNAM, Campus Morelos, Av. Universidad 1001, Col. Chamilpa, Cuernavaca C.P. 62210, Morelos, Mexico; nildita1985@gmail.com 6 Catedras Conacyt-Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Campus Morelos, Av. Universidad 1001, Col. Chamilpa, Cuernavaca C.P. 62210,Morelos, Mexico; ayixon.sanchez@ibt.unam.mx * Correspondence: maria.sanchez@uaem.mx † These authors contributed equally to this work. Abstract: Aspergillus sydowii is a moderate halophile fungus extensively studied for its biotechno- logical potential and halophile responses, which has also been reported as a coral reef pathogen. In a recent publication, the transcriptomic analysis of this fungus, when growing on wheat straw, showed that genes related to cell wall modification and cation transporters were upregulated under hypersaline conditions but not under 0.5 M NaCl, the optimal salinity for growth in this strain. This led us to study osmolyte accumulation as a mechanism to withstand moderate salinity. In this work, we show that A. sydowii accumulates trehalose, arabitol, mannitol, and glycerol with different temporal dynamics, which depend on whether the fungus is exposed to hypo- or hyperosmotic stress. The transcripts coding for enzymes responsible for polyalcohol synthesis were regulated in a stress-dependent manner. Interestingly, A. sydowii contains three homologs (Hog1, Hog2 and MpkC) of the Hog1 MAPK, the master regulator of hyperosmotic stress response in S. cerevisiae and other fungi. We show a differential regulation of these MAPKs under different salinity conditions, includ- ing sustained basal Hog1/Hog2 phosphorylation levels in the absence of NaCl or in the presence of 2.0 M NaCl, in contrast to what is observed in S. cerevisiae. These findings indicate that halophilic fungi such as A. sydowii utilize different osmoadaptation mechanisms to hypersaline conditions. Keywords: halophile; osmolyte; osmotic shock; HOG; Aspergillus; extremophile 1. Introduction Halophilic and halotolerant microorganisms, which thrive in saline environments, adapt strategies to cope with high concentrations of sodium chloride. The high ionic force in these environments provokes the inactivation of proteins and the osmotic pressure causes J. Fungi 2021, 7, 414. https://doi.org/10.3390/jof7060414 https://www.mdpi.com/journal/jof