Molecular cloning, characterization and regulation by cadmium of a superoxide dismutase from the ectomycorrhizal fungus Paxillus involutus

The gene encoding a superoxide dismutase (PiSOD) was cloned by suppressive subtractive hybridization from cDNA library of the ectomycorrhizal fungus, Paxillus involutus, grown under cadmium-stress conditions. The encoded prot ein was presumed to be localized in the peroxisomes because it contained a C-terminal peroxisomal localization peptide (SKL) and lacked an N-terminal mitochondrial transit peptide. Complementation of an Escherichia coli SOD n ull strain that is unable to grow in the presence of paraquat or cadmium in dicated that cloned Pisod encoded a functional superoxide dismutase. Sensit ivity of PiSOD activity to H2O2 but not KCN, and sequence homologies to oth er SODs strongly suggest that it is a manganese-containing superoxide dismu tase. Monitoring PiSOD transcript, immunoreactive polypeptide and superoxid e dismutase activity following cadmium stress suggests that the principal l evel of control is post-translational. This is, to our knowledge, the first insight in the characterization of molecular events that take place in an ectomycorrhizal fungus during exposure to heavy metals.