IONIC HOMEOSTASIS, CELLULAR STRESS AND GENOMICS GROUP
General Goals
The “Ionic Homeostasis, Cellular Stress and Genomics” group focuses on identifying the molecular bases of monovalent cation (H⁺, K⁺, Na⁺) homeostasis and tolerance mechanisms to abiotic stresses such as drought, salinity, heat, cold, acidity, and oxidative environments. These two aspects are closely linked: cellular stress triggers early signals based on opposing fluxes of H⁺ and K⁺ and changes in plasma membrane potential. Furthermore, H⁺ and K⁺ transport regulates stress tolerance, growth, and cell death. Notably, biological phenomena are often better understood under stress, which reveals the most powerful defense tools of living organisms.

The model systems used in these studies are the yeast Saccharomyces cerevisiae and the plant Arabidopsis thaliana, which share basic mechanisms of ionic homeostasis and stress tolerance and offer complementary experimental advantages.

We employ two main methodological approaches:
a) Functional genomics to identify genes crucial for ionic homeostasis and abiotic stress tolerance.
b) Molecular biology and biochemistry to decipher the mechanisms of action of the proteins encoded by these genes.

Functional genomics in our group includes:

Global gene expression profiling using microarrays.

Genome-wide mutational analysis and selection screens.

In both approaches, yeasts or Arabidopsis are exposed to stress conditions. We identify:
a) Stress-regulated genes, which define transcriptional response mechanisms. However, not all relevant genes are transcriptionally regulated, and not all regulated genes are biologically relevant.
b) Stress-tolerant mutants, selected using marked mutants (plasmid-based in yeast or T-DNA tagged in Arabidopsis), allowing easy identification of the responsible genes.

These approaches lead to the discovery of novel stress-response genes and mechanisms in yeast and Arabidopsis, providing biotechnological tools to improve stress tolerance in crop plants and industrial yeast strains, and resulting in patents.

BACKGROUND AND PAST ACHIEVEMENTS
Ramón Serrano (RS) received his scientific training under three prominent figures in modern biology: Spanish enzymologist Alberto Sols, American membrane biochemist Efraim Racker, and molecular biologist Gerald R. Fink. For over 25 years, RS’s research has focused on the mechanisms of cation (H⁺, K⁺, Na⁺) homeostasis and their role in regulating cell growth and stress tolerance.

RS’s first major contribution as an independent scientist was the characterization of the plasma membrane proton pump in yeast and plants. Unlike animal cells, which use the Na⁺/K⁺-ATPase described by Nobel laureate Jens C. Skou, fungi and plants use a distinct electrogenic H⁺-ATPase. In the early 1980s, RS’s biochemical work demonstrated the presence of this pump via purification and reconstitution in ATP-driven proton-pumping proteoliposomes.

RS also pioneered the isolation and characterization of the genes encoding the H⁺-ATPase—first in yeast (1986) and then in Arabidopsis (1989). Targeted and random mutagenesis of the yeast H⁺-ATPase gene revealed key residues and functional domains responsible for the kinase and phosphatase reactions in the catalytic cycle. Recent structural studies on homologous enzymes, like the sarcoplasmic reticulum Ca²⁺-ATPase, have confirmed these models.

Genetic manipulation of the yeast H⁺-ATPase established a correlation between pump activity and cell growth, through nutrient uptake and intracellular pH regulation—a key factor in the G0/G1 transition in the cell cycle. These findings have been partially extrapolated to animal and plant systems.

CURRENT RESEARCH LINES
a) Intracellular acidification
Changes in intracellular H⁺ concentration (pHi) serve as a signal in various processes such as growth, cell death, and stress responses. Our group described one of the few known molecular pHi-sensing systems: the interaction between Ppz1 phosphatase and its regulator Hal3, which activates the K⁺ transporter Trk1 under low pH. Recent yeast results suggest that mild acidification inhibits amino acid transport and tRNA charging, generating uncharged tRNAs. In Arabidopsis, we have identified new regulators of K⁺ transport (QSO2, ROF2, WAT1), and demonstrated that abscisic acid (ABA) inhibits the root H⁺-ATPase, causing intracellular acidification and K⁺ efflux via GORK, contributing to growth inhibition.

b) Polyamines and lithium toxicity
Polyamines and lithium are toxic cations with minimal osmotic effects. Using norspermidine, we identified Arabidopsis QSO2 as a positive regulator of K⁺ loading in the xylem, which indirectly regulates toxic cation transport. We also investigate millimolar polyamine toxicity, linked to oxidative stress and protein denaturation. We’ve shown that lithium toxicity in Arabidopsis involves ethylene signaling, with catalase mutants showing lithium resistance via ethylene insensitivity.

c) Seed longevity and aging stress
We use accelerated aging in Arabidopsis seeds to identify mutants with enhanced longevity. Overexpression of candidate genes (AGL18, ZFHD2, COG1, RSL1) improves seed tolerance to aging by reinforcing the seed coat with suberin.

d) Sugar metabolism signaling
H⁺-ATPase activity is regulated by sugar metabolism, possibly through glycolytic intermediates that inhibit yeast protein phosphatase 1 in vitro. We’re testing this hypothesis.

e) Cold tolerance in brewing yeasts
Saccharomyces pastorianus ferments at low temperatures (10–14°C), essential for proper beer flavor. Cold tolerance appears linked to nutrient transporter stability. We’re constructing a gene library from a sequenced lager yeast and screening for cold-tolerance genes in lab yeast strains.

f) TOR, H⁺-ATPase, and K⁺ transport
The TOR kinase is a master regulator of cell growth. We hypothesize that it positively regulates the H⁺-ATPase and K⁺ transport. Initial experiments suggest transcriptional regulation, and we are now examining changes in enzyme levels and activity.

g) H₂O₂ and programmed cell death
In yeast, glucose addition without nutrients triggers H₂O₂ accumulation and cell death. K⁺ addition or reduced H⁺-ATPase activity suppresses H₂O₂ production. We suspect an unidentified NAD(P)H oxidase is responsible. H₂O₂ appears to activate K⁺ efflux (via TOK1, ENA1, NHA1), leading to vacuolar lysis and autolysis—a potential altruistic mechanism where degraded cellular content supports neighboring cells.

• Martinez F, Arif A, Nebauer S, Bueso E, Ali R, Montesinos,C, Brunaud V, Munoz-Bertomeu J, Serrano R (2015)
  A fungal transcription factor gene is expressed in plants from its own promoter and improves drought tolerance

  Planta 242: 39-52

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• Martínez F, Arif A, Nebauer SG, Bueso E, Ali R, Montesinos C, Brunaud V, Muñoz-Bertomeu J, Serrano R (2015)
  A fungal transcription factor gene is expressed in plants from its own promoter and improves drought tolerance

  Planta 242: 39-52

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• Anoman AD, Munoz-Bertomeu J, Rosa-Tellez S, Flores-Tornero M, Serrano R, Bueso E, Fernie AR, Segura J, Ros R (2015)
  Plastidial Glycolytic Glyceraldehyde–Phosphate Dehydrogenase Is an Important Determinant in the Carbon and Nitrogen Metabolism of Heterotrophic Cells in Arabidopsis

  Plant Physiology 169: 1619-1637

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• Faus I, Zabalza A, Santiago J, Nebauer SG, Royuela M, Serrano R, Gadea J (2015)
  Protein kinase GCN mediates responses to glyphosate in Arabidopsis

  BMC Plant Biology 15: 14

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• Sayas Enric,Garcia-Lopez Federico,Serrano Ramon (2015)
  Toxicity mutagenicity and transport in Saccharomyces cerevisiae of three popular DNA intercalating fluorescent dyes

  Yeast 32: 595-606

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• Vicent I, Navarro A, Mulet JM, Sharma S, Serrano R (2015)
  Uptake of inorganic phosphate is a limiting factor for Saccharomyces cerevisiae during growth at low temperatures

  FEMS Yeast Research 15: fov008

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• Bueso E, Ibañez C, Sayas E, Muñoz-Bertomeu J, Gonzalez-Guzman M, Rodriguez PL, Serrano R (2014)
  A forward genetic approach in Arabidopsis thaliana identifies a RING-type ubiquitin ligase as a novel determinant of seed longevity

  Plant Science 215–216: 110–116

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• Planes MD, Niñoles R, Rubio L, Bissoli G, Bueso E, García-Sánchez MJ, Alejandro S, Gonzalez-Guzmán M, Hedrich R, Rodriguez PL, Fernández JA, Serrano R (2014)
  A mechanism of growth inhibition by abscisic acid in germinating seeds of Arabidopsis thaliana based on inhibition of plasma membrane H+-ATPase and decreased cytosolic pH, K+ and anions

  Journal of Experimental Botany 66: 813-825

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• Fasano R,Gonzalez N , Tosco A ,Dal Piaz F ,Docimo T , Serrano R ,Grillo S ,Leone A ,Inze D (2014)
  Role of Arabidopsis UV RESISTANCE LOCUS 8 in Plant Growth Reduction under Osmotic Stress and Low Levels of UV-B

  MOLECULAR PLANT 7: 773-791

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Nuevos genes reguladores de la tolerancia al estrés abiótico en Arabidopsis.
Año:2015
Nombre : Felix Martínez Macías
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Jesús Muóz Bertomeu
Tipo: Tesis Doctorales

Nuevas funciones de Gcn2p en respuestra a estrés ácido y genotóxico.
Año:2014
Nombre: Rafael Aparicio Sanchis
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Jose Ramón Murguía.
Tipo: Tesis Doctorales

Hipusinación del factor de traducción eIF5A dependiente de poliaminas.
Año:2014
Nombre: Borja Belda Palazón
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Alejandro Ferrando.
Tipo: Tesis Doctorales

Evolución genómica por diseño molecular de levaduras industriales
Año:2013
Nombre: Daniele Sani
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Alfonso Navarro Marzal.
Tipo: Tesis Doctorales

Prolyl isomerases are important determinants of intracellular pH homeostasis in Arabidopsis thaliana.
Año:2012
Nombre: Gaetano Bissoli
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Jose Miguel Mulet
Tipo: Tesis Doctorales
Biología molecular de la regulación de la homeostasis de pH en Arabidopsis thaliana.

Año:2011
Nombre: Regina Niñoles Rodenes
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Santiago Alejandro Martínez
Tipo: Tesis Doctorales
Caracterización de la regulación de la protón-ATPasa Pma1 por parte de la ruta TOR en levadura.

Año:2010
Nombre: Marc Cabedo López
Universidad: Universitat Politècnica de València
Tipo: Trabajos de Fin de Carrera
Estudio de los mecanismos de la regulación de la homeostasis iónica: análisis fisiológico y transcriptómico del mutante hal4 hal5 de Saccharomyces cerevisiae.

Año:2009
Nombre: Jorge Pérez Valle
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Lynne Yenush.
Tipo: Tesis Doctorales
La biosíntesis del CoA y su papel esencial en el establecimiento de la plántula, en la respuesta al estrés osmótico/salino y en el almacenamiento de lípidos en Arabidopsis thaliana.

Año:2009
Nombre: Silvia Rubio Novella
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Pedro L. Rodríguez.
Tipo: Tesis Doctorales
Aislamiento e identificación de genes de Saccharomyces cerevisiae implicados en la tolerancia a frío

Año:2009
Nombre: Isabel Vicent Gonzáliez
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Alfonso Navarro Marzal
Tipo: Tesis Doctorales
La tolerancia a litio del mutante cat2 de Arabidopsis revela una estrecha relación entre estrés oxidativo y etileno.

Año:2008
Nombre: Eduardo Bueso Ródenas
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano
Tipo: Tesis Doctorales
Cellular implications of alterations in potassium homeostasis in Saccharomyces cerevisiae

Año:2007
Nombre: Stephanie Merchan
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Lynne Yenush
Tipo: Tesis Doctorales
Respuesta transcripcional al estrés hídrico en mandarino: Estudio genómico-funcional con micromatrices de cDNA.

Año:2007
Nombre: Jacinta Gimeno Romeu
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y José Gadea
Tipo: Tesis Doctorales
Identificación de mutantes de Arabidopsis thalianarsistentes a norespermidina. Clonación y caracterización de una sulfidril oxidasa.

Año:2007
Nombre: Santiago Alejandro Martínez
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Pedro L. Rodríguez
Tipo: Tesis Doctorales
Genética molecular de la biosíntesis del ácido abscísico. Clonación y caracterización del gen ABA2

Año:2005
Nombre: Miguel Gonzalez Guzman
Universidad: Universitat Politècnica de València
Dirigida por: Ramón Serrano y Pedro L. RodríguezTipo:
Tesis Doctorales