Functional and phylogenetic implications of septal pore ultrastructure in the ascoma of Neolecta vitellina

Abstract

Neolecta represents the earliest derived extant ascomycete lineage (Taphrinomycotina) to produce ascomata. For this reason the genus has been of interest with regard to ascoma evolution in ascomycetes. However, the evidence is equivocal regarding whether the Neolecta ascoma is homologous or analogous to ascomata produced in the later derived ascomycete lineages (Pezizomycotina). We investigated phylogenetically informative septal pore ultrastructure of Neolecta vitellina to compare with Pezizomycotina. We found that crystalline bodies that block nonascogenous septal pores in Neolecta differ from Woronin bodies, a synapomorphy for the Pezizomycotina, in three ways: (i) vacuolar origin, (ii) associated material and (iii) being loosely membrane bound. We also observed a unique type of membranous material within the septal pore, as well as distant from the septal pore, that appears to be associated with the endoplasmic reticulum. The vacuolar crystals and membranous material might have a function analagous to septal pore structures (e.g. Woronin bodies, lamellate structures) in the Pezizomycotina. Morphological evidence from our study supports an independently derived septal pore-occluding structure in the Neolecta lineage.