Structural character evolution in Pucciniomycotina: mitosis, septa, and hyphal branch initiation in two Helicogloea species.

Early diverging taxa of Ascomycota and Basidiomycota share similarities in subcellular characters of the spindle pole body (SPB), nuclear division, and septal pore apparatus, but our understanding of character evolution is incomplete because of the limited number of structural studies within the earliest diverging subphyla of Dikarya, Taphrinomycotina and Pucciniomycotina. Two species of Helicogloea (Atractiellomycetes) were analyzed for these characters and provide data on SPB and nuclear division for an additional class of Pucciniomycotina. A detailed analysis of septal pore apparatus for the Helicogloea species permits comparisons with those of other Pucciniomycotina and Ascomycota. The endogenous origin of hyphal branches is shown to occur in a third class of Pucciniomycotina. The full set of characters supports a close relationship between Atractiellomycetes and Pucciniomycetes.

An overview of the higher level classification of Pucciniomycotina based on combined analyses of nuclear large and small subunit rDNA sequences.

In this study we provide a phylogenetically based introduction to the classes and orders of Pucciniomycotina (= Urediniomycetes), one of three subphyla of Basidiomycota. More than 8000 species of Pucciniomycotina have been described including putative saprotrophs and parasites of plants, animals and fungi. The overwhelming majority of these (approximately 90%) belong to a single order of obligate plant pathogens, the Pucciniales (= Uredinales), or rust fungi. We have assembled a dataset of previously published and newly generated sequence data from two nuclear rDNA genes (large subunit and small subunit) including exemplars from all known major groups in order to test hypotheses about evolutionary relationships among the Pucciniomycotina. The utility of combining nuc-lsu sequences spanning the entire D1-D3 region with complete nuc-ssu sequences for resolution and support of nodes is discussed. Our study confirms Pucciniomycotina as a monophyletic group of Basidiomycota. In total our results support eight major clades ranked as classes (Agaricostilbomycetes, Atractiellomycetes, Classiculomycetes, Cryptomycocolacomycetes, Cystobasidiomycetes, Microbotryomycetes, Mixiomycetes and Pucciniomycetes) and 18 orders.

Mitosis in the yeast phase of the basidiomycetes Bensingtonia yuccicola and Stilbum vulgare and its phylogenetic implications.

Phylogenetic studies of yeasts rely on an extensive molecular and biochemical data set, but structural characters are scarce. Details of mitosis in yeasts have been studied with transmission electron microscopy and immunofluorescence. Of these two methods immunofluorescence is faster and easier and yields sufficient detail for cytological comparisons. Only three basidiomycetous yeasts have been studied thus far with immunofluorescence. Mitosis in budding cells of ascomycetous yeasts occurs in the parent, while in basidiomycetous yeasts, except in Agaricostilbum pulcherrimum, it occurs in the bud. Mitosis in additional yeasts in the Agaricostilbomycetidae of the Urediniomycetes was observed using immunofluorescence localization of freeze-substituted material. In Stilbum vulgare, mitosis occurred in the parent, but in Bensingtonia yuccicola it occurred in the bud as in most other basidiomycetous yeasts. Stilbum vulgare also had predominantly binucleate yeast cells. Nuclear small subunit rDNA sequence data showed that A. pulcherrimum and S. vulgare are more closely related to each other than to B. yuccicola within the Agaricostilbomycetidae. Based on the few taxa examined, mitotic and cytoskeletal characters provide phylogenetic information.