Phylogenetic diversity of stress signalling pathways in fungi.
BACKGROUND
Microbes must sense environmental stresses, transduce these signals and mount protective responses to survive in hostile environments. In this study we have tested the hypothesis that fungal stress signalling pathways have evolved rapidly in a niche-specific fashion that is independent of phylogeny. To test this hypothesis we have compared the conservation of stress signalling molecules in diverse fungal species with their stress resistance. These fungi, which include ascomycetes, basidiomycetes and microsporidia, occupy highly divergent niches from saline environments to plant or mammalian hosts.


RESULTS
The fungi displayed significant variation in their resistance to osmotic (NaCl and sorbitol), oxidative (H2O2 and menadione) and cell wall stresses (Calcofluor White and Congo Red). There was no strict correlation between fungal phylogeny and stress resistance. Rather, the human pathogens tended to be more resistant to all three types of stress, an exception being the sensitivity of Candida albicans to the cell wall stress, Calcofluor White. In contrast, the plant pathogens were relatively sensitive to oxidative stress. The degree of conservation of osmotic, oxidative and cell wall stress signalling pathways amongst the eighteen fungal species was examined. Putative orthologues of functionally defined signalling components in Saccharomyces cerevisiae were identified by performing reciprocal BLASTP searches, and the percent amino acid identities of these orthologues recorded. This revealed that in general, central components of the osmotic, oxidative and cell wall stress signalling pathways are relatively well conserved, whereas the sensors lying upstream and transcriptional regulators lying downstream of these modules have diverged significantly. There was no obvious correlation between the degree of conservation of stress signalling pathways and the resistance of a particular fungus to the corresponding stress.


CONCLUSIONS
Our data are consistent with the hypothesis that fungal stress signalling components have undergone rapid recent evolution to tune the stress responses in a niche-specific fashion.
Nikolaou
Elissavet
E
Aberdeen Fungal Group, School of Medical Sciences, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen, AB25 2ZD, UK. e.nikolaou@abdn.ac.uk
Agrafioti
Ino
I
Stumpf
Michael
M
Quinn
Janet
J
Stansfield
Ian
I
Brown
Alistair J P
AJ
D001557:Benzenesulfonates / Q000494:pharmacology; D002176:Candida albicans / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D002473:Cell Wall / Q000187:drug effects / Q000378:metabolism; D003224:Congo Red / Q000494:pharmacology; D004271:DNA, Fungal / Q000235:genetics; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D016681:Genome, Fungal; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009997:Osmotic Pressure; D018384:Oxidative Stress; D010802:Phylogeny; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics*; D012965:Sodium Chloride / Q000494:pharmacology; D013012:Sorbitol / Q000494:pharmacology; D024483:Vitamin K 3 / Q000494:pharmacology
D001557:Benzenesulfonates; D004271:DNA, Fungal; D005656:Fungal Proteins; D003224:Congo Red; D012965:Sodium Chloride; D013012:Sorbitol; D024483:Vitamin K 3; C007061:C.I. Fluorescent Brightening Agent 28; D006861:Hydrogen Peroxide