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.