LARGE-SUBUNIT RIBOSOMAL-RNA SEQUENCE OF THE CHYTRIDIOMYCETE BLASTOCLADIELLA-EMERSONII, AND IMPLICATIONS FOR THE EVOLUTION OF ZOOSPORIC FUNGI

The 5.8S and 28S ribosomal RNA sequences of the chytridiomycete Blasto cladiella emersonii were determined. These data were combined with 18S rRNA sequences in order to carry out a phylogenetic analysis based on distance matrix, parsimony, and maximum likelihood methods. The new d ata confirmed that chytridiomycetes are true fungi and not protists, a s was already suggested on the basis of biochemical, ultrastructural, and 18S rRNA data. Within the fungal clade, B. emersonii formed the fi rst line of divergence. The position of the fungi within the eukaryoti c ''crown'' taxa was also reassessed, and the alveolate-stramenopile c luster appeared as their sister group. The stramenopiles also comprise a number of zoosporic fungi, which resemble chytridiomycetes in so ma ny respects, e.g., production of motile spores, thallus morphology, an d absorptive nutrition, that they have been classified together with t hem in the past. This suggests that the possible common ancestor of th e fungi, stramenopiles, and alveolates may have been a zoosporic fungu s, which would mean that zoosporic fungi are paraphyletic instead of p olyphyletic as previously suggested.