Global gene expression profiles for life stages of the deadly amphibian pathogenBatrachochytrium dendrobatidis

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Abstract
Amphibians around the world are being threatened by an emerging pathogen, the chytrid fungusBatrachochytrium dendrobatidis(Bd). Despite intensive ecological study in the decade sinceBdwas discovered, little is known about the mechanism by whichBdkills frogs. Here, we compare patterns of global gene expression in controlled laboratory conditions for the two phases of the life cycle ofBd: the free-living zoospore and the substrate-embedded sporangia. We find zoospores to be transcriptionally less complex than sporangia. Several transcripts more abundant in zoospores provide clues about how this motile life stage interacts with its environment. Genes with higher levels of expression in sporangia provide new hypotheses about the molecular pathways involved in metabolic activity, flagellar function, and pathogenicity inBd. We highlight expression patterns for a group of fungalysin metallopeptidase genes, a gene family thought to be involved in pathogenicity in another group of fungal pathogens that similarly cause cutaneous infection of vertebrates. Finally we discuss the challenges inherent in developing a molecular toolkit for chytrids, a basal fungal lineage separated by vast phylogenetic distance from other well characterized fungi.