Characterization of a salt-induced DhAHP, a gene coding for alkyl hydroperoxide reductase, from the extremely halophilic yeast Debaryomyces hansenii

Abstract

BackgroundDebaryomyces hansenii is one of the most salt tolerant species of yeast and has become a model organism for the study of tolerance mechanisms against salinity. The goal of this study was to identify key upregulated genes that are involved in its adaptation to high salinity.ResultsBy using forward subtractive hybridization we have cloned and sequenced DhAHP from D. hansenii that is significantly upregulated during salinity stress. DhAHP is orthologous to the alkly hydroperoxide reductase of the peroxiredoxin gene family, which catalyzes the reduction of peroxides at the expense of thiol compounds. The full-lengthed cDNA of DhAHP has 674 bp of nucleotide and contains a 516 bp open reading frame (ORF) encoding a deduced protein of 172 amino acid residues (18.3 kDa). D. hansenii Ahp is a cytosolic protein that belongs to the Ahp of the 1-Cys type peroxiredoxins. Phylogentically, the DhAhp and Candida albicans Ahp11 (Swiss-Prot: Q5AF44) share a common ancestry but show divergent evolution. Silence of its expression in D. hansenii by RNAi resulted in decreased tolerance to salt whereas overexpression of DhAHP in D. hansenii and the salt-sensitive yeasts Saccharomyces cereviasiae and Pichia methanolica conferred a higher tolerance with a reduced level of reactive oxygen species.ConclusionIn conclusion, for the first time our study has identified alkly hydroperoxide reductase as a key protein involved in the salt tolerance of the extremely halophilic D. hansenii. Apparently, this enzyme plays a multi-functional role in the yeast's adaptation to salinity; it serves as a peroxidase in scavenging reactive oxygen species, as a molecular chaperone in protecting essential proteins from denaturation, and as a redox sensor in regulating H2O2-mediated cell defense signaling.

DhARO4 induction and tyrosine nitration in response to reactive radicals generated by salt stress in Debaryomyces hansenii

“…We assume that NaCl stress leads to oxidative stress; it can then be expected that 3.5 m NaCl leads to a higher level of ROS, just as it occurs during oxidative stress where ROS levels increase as the oxidant increases. However, another important factor in the ROS generation is the exposure time; Knöbel et al () showed in human cells exposed to ferric nitrilotriacetate (Fe‐NTA) that ROS generation is time and dose dependent, which may explain why our results are similar to those reported by Chao et al ().…”

“…They found an upregulation of genes known to express under osmotic stress; genes related to protein synthesis and maintenance and, remarkably, genes related to mitochondrial functions. Chao et al () reported DhAHP as a novel gene that significantly conferred salt stress tolerance in this yeast; they also found that the overexpression of DhAHP , an alkyl hydroperoxide reductase, diminished the accumulation of reactive oxygen species (ROS) under hypersaline stress and that repression of DhAHP expression decreased the tolerance to salt stress. Lately, it was reported that NaCl protects against oxidative stress in D. hansenii (Navarrete et al, ).…”

Expression of salt-induced 2-Cys peroxiredoxin from Oryza sativa increases stress tolerance and fermentation capacity in genetically engineered yeast Saccharomyces cerevisiae

“…According to studies from the literature, overexpression of the homologous 2-Cys Prx gene encoding ubiquitous thiol-specific peroxidases increased stress tolerance and redox homeostasis in several organisms. For example, salt-induced Debaryomyces hansenii AHP (DhAHP, Prx isoform) expression conferred higher salt tolerance by reducing the cellular ROS level in D. hansenii, S. cerevisiae, and Pichia methanolica (Chao et al 2009). Overexpression of A. thaliana 2-Cys Prx (At2-Cys Prx; accession no.…”

The halotolerant Debaryomyces hansenii, the Cinderella of non‐conventional yeasts

“…Gene DhAHP1 , coding for a cytosolic alkyl hydroperoxide reductase, is regulated under saline conditions, and the corresponding protein has been also correlated with salt resistance (Chao et al , ). Silencing of its expression in D. hansenii resulted in decreased tolerance, while overexpression, both in S. cerevisiae and in D. hansenii , conferred enhanced tolerance to salinity.…”

“…Silencing of its expression in D. hansenii resulted in decreased tolerance, while overexpression, both in S. cerevisiae and in D. hansenii , conferred enhanced tolerance to salinity. The fact that overexpressing transformants exhibited reduced levels of reactive oxygen species (ROS) under salt stress suggests that DhAhp1 may play a key role in adaption to high salinity by scavenging ROS, serving as chaperone and mediating oxidative stress signalling (Chao et al , ).…”