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HGT or Something More Interesting? Phylogeny of a Family of Enzymes Including One for a Bioprotective Alkaloid Produced by Epichloë spp.

Christopher Schardl: University of Kentucky

<div>Fungal genes encoding biosynthetic enzymes for specialized metabolites (SM) are often reported as examples of horizontal gene transfer (HGT) between highly divergent fungal taxa, but multiple paralogy (gene duplication) and loss events are the likeliest alternative. Among the suggested HGT examples are genes for lolines, anti-insect alkaloids produced by grass-symbiotic <em>Epichloë </em>species. One loline biosynthesis enzyme, LolC, is a member of a well-characterized family including several housekeeping enzymes. I conducted phylogenetic analysis of this family to investigate whether SM genes tend to exhibit more paralogy and loss than do related housekeeping genes. Included were all LolC-related genes in genomes of 24 species from five classes of Ascomycota. The clade for each of three housekeeping genes contained a single representative from each genome, and phylogenies within these clades were mostly consistent with each other and currently accepted species relationships. In contrast, related SM genes and genes with unknown functions exhibited extensive paralogy. These included a well-supported clade of 23 genes that had five sets of paralogs, were absent from several genomes, and had a substantially different phylogeny from those of housekeeping genes. I conclude that duplications and losses of non-housekeeping genes, together with selection for their abundance or paucity in different fungal groups as observed for loline genes, may be much more important than HGT in evolution and niche specialization of plant-pathogenic and plant-symbiotic fungi.</div>