The phylogeny of plant and animal pathogens in the Ascomycota

0885-5765/0 * To who berbee@inte What makes a fungus pathogenic? In this review, phylogenetic inference is used to speculate on the evolution of plant and animal pathogens in the fungal PhylumAscomycota. A phylogeny is presented using 297 18S ribosomal DNA sequences from GenBank and it is shown that most known plant pathogens are concentrated in four classes in the Ascomycota. Animal pathogens are also concentrated, but in two ascomycete classes that contain few, if any, plant pathogens. Rather than appearing as a constant character of a class, the ability to cause disease in plants and animals was gained and lost repeatedly. The genes that code for some traits involved in pathogenicity or virulence have been cloned and characterized, and so the evolutionary relationships of a few of the genes for enzymes and toxins known to play roles in diseases were explored. In general, these genes are too narrowly distributed and too recent in origin to explain the broad patterns of origin of pathogens. Co-evolution could potentially be part of an explanation for phylogenetic patterns of pathogenesis. Robust phylogenies not only of the fungi, but also of host plants and animals are becoming available, allowing for critical analysis of the nature of co-evolutionary warfare. Host animals, particularly human hosts have had little obvious e€ect on fungal evolution and most cases of fungal disease in humans appear to represent an evolutionary dead end for the fungus. Plants have been important in the evolution of fungi, and the rapid nature of co-evolutionary change might partially explain the lack of obvious, global characters uniting all plant pathogens. *c 2001 Academic Press