Origin of laccase gene structural diversity in edible mushrooms

Laccase genes have been found in fungi, plants, insects and bacteria. In Basidiomycetes, the number of laccase genes ranges from 0 to 17. The role of these genes is not well known. It seems to be important in fungal interaction, development, melanine synthesis, human and plant pathogenesis, [ectomycorrhizal association and nutrition of the fungi]. Their role as ligninmodifying enzymes is controversial. Laccase phylogeny already published is not congruent with species phylogeny. Phylogeny of gene is generally deduced from analyse of aligned sequences of nucleotides or amino acids. Presence of indels, position of introns can give complementary information. To better understand the origin and evolution of Basidiomycete laccase genes, we studied the structure of diverse multi copper oxidase genes in different phylum of Eukaryotes, in basidomycetes and in Agaricus bisporus. A mutation has been conserved in all basidiomycete laccases and constitutes a molecular synapomorphy for basidiomycete laccase genes. At least three main laccase subfamilies (A, B and C) are present in Polyporales and Agaricales. In A. bisporus the 4 new laccase genes we have sequenced (lcc3-lcc6) belong to a new sub-family for this species. Cladogram of laccase genes from edible mushrooms built with Dollo parsimony of intron position is congruent with dendrograms built with homologous amino acid sequences, but is not identical. Some consequences on the evolution of laccase genes and their diversity are discussed