Chapter 29 : Fungal Genomes and Insights into the Evolution of the Kingdom

Abstract:

Studies of fungal evolution require an understanding of the phylogenetic relationships and relative evolutionary divergence of organisms. The first approaches to organizing fungi into related groups relied on morphological characteristics ( 1 ). These approaches provided a broad framework to organize fungal organisms for taxonomic classification based on recognizable morphological characteristics such as spore shape, asexual and sexual structures, and in mushroom-forming fungi, the shape and presence/absence of gills, veil attachments, and spore color. In zoosporic chytrid fungi the characteristics seen by scanning electron microscopy of zoospores reveal that the ultrastructure of the kinetosomes and flagellum are all diagnostic for the classification of many lineages ( 2 ). However, the microscopic nature of many fungi and especially of yeast-forming fungi with limited visible differences, and the prevalence of convergent evolution to homoplasies or similar characteristics across a tree, has made taxonomic classification of groups of fungi difficult or easily misled. The invention and application of DNA sequencing ( 3 ) and PCR ( 4 ) and the development of primers to amplify fungal rRNA enabled a new era of molecular phylogenetic studies in fungi ( 5 ). These approaches provided invaluable information that was used to resolve the major fungal lineages ( 2 , 6 – 20 ) and the delineation of species ( 21 – 24 ). Using DNA approaches to study the entire fungal tree of life provided new insight into the order of branching of major groups and the timing of morphological changes such as the loss of the flagellum found in zoosporic fungi ( 14 , 17 , 18 , 25 ).