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.

• crystal
• fungal evolution
• septal pore occlusion
• Taphrinomycotina
• Woronin body

Acknowledgments

We thank R. Roberson and two anonymous reviewers for their helpful suggestions. We are grateful for the help of G. Jedd for valuable discussions regarding Woronin bodies during this study and for his suggestion to induce crystal plugging through wounding before fixation. This research was financed through an NSF award DEB-0732550 to DJ McLaughlin for work on the Assembling the Fungal Tree of Life project. We thank Esther McLaughlin for collecting the Neolecta specimens used in this study, Gail Celio and the University of Minnesota Imaging Center for assistance with TEM and Trevor Wennblum and the University of Minnesota Supercomputing Institute for assistance with the SBD and access to Sequencher. The Minnesota DNR is thanked for permission to collect and the Bell Museum of Natural History is thanked for curation.