Specific regions in the Sod1 locus of the ericoidmycorrhizal fungus Oidiodendron maius from metal-enriched soils show a different sequence polymorphism

The huge diversity of fungi may reflect both the heterogeneity of the niches they occupy and the diverse stresses they must cope with. In order to investigate the genetic and functional diversity in the ericoid mycorrhizal fungus Oidiodendron maius subjected to heavy metal stress, we isolated O. maius strains from a serpentine site naturally enriched by heavy metals. Despite the high Cr and Ni soil concentrations, a high level of diversity was found in the serpentine fungal community. The growth of these isolates in the presence of different metal contaminants identified some tolerant strains, suggesting a site-specific adaptation. To investigate within-species gene divergence in stressful environments, we then compared the sequence polymorphism of a neutral (internal transcribed spacer) and a functional (Cu,ZnSOD) gene in O. maius isolates derived from the serpentine site, from a site heavily polluted with industrial wastes and from unpolluted sites. For all isolates tested, the polymorphism was higher in the nucleotide sequence of the functional gene. However, when compared with isolates from the serpentine area, isolates from industrially polluted sites showed a significantly higher polymorphism in the Cu,ZnSOD promoter region, suggesting that environmental stress may influence the rate of mutations in specific regions of the Sod1 locus.