Perithecium morphogenesis in Neurospora crassa and Sordaria macrospora
Date
28/11/2013Author
Topham, Kathryn Mary
Lord, Kathryn Mary
Metadata
Abstract
Multicellular development in fungi is fundamentally different from that of animals or
plants. In filamentous fungi, multicellular structures are formed by aggregation and
adhesion of hyphae, followed by septation and specialisation of hyphal compartments
within the aggregate. The perithecium, a flask-shaped sexual fruitbody produced by
both Neurospora crassa and Sordaria macrospora, provides a model system in which
to study fungal multicellular development.
This study presents a detailed description of the morphological stages of perithecial
morphogenesis in N. crassa and S. macrospora and its early stages, the ascogonial
and protoperithecial stages, using a range of microscopical techniques. Details of the
development of several mutants impaired in perithecial development are described,
including: gene-deletion mutants of all nine mitogen-activated protein (MAP) kinases
conserved in N. crassa; and three mutants pro22, pro40 and pro41 of S. macrospora,
and their corresponding gene-deletions in N. crassa.
The results confirm that all three MAP kinase cascades are required for sexual development.
However, only the pheromone response and cell-wall integrity MAP kinase
pathways, but not the osmoregulatory MAP kinase pathway, are essential for hyphal
cell fusion. Evidence of cell fusion-related processes, regulated through MAP kinase
signalling, have been identified as novel features important for the construction of
fertilisable protoperithecia. These cell-fusion related processes include extracellular
matrix deposition, hyphal attachment and envelopment.
A novel phenotype of S. macrospora with defective ascogonial septation is presented.
This pro22 mutant also has impaired hyphal cell fusion and produces only small, defective
protoperithecia. The pro22 gene encodes a protein that is highly conserved
throughout eukaryotes. Live-cell imaging revealed that this PRO22 protein is localised
in the dynamic tubular and vesicular vacuolar-network of the colony periphery and in
ascogonia. PRO22 is absent from the large spherical vacuoles in the vegetative hyphae
of the sub-peripheral region of the colony. This points to a specific role of PRO22
in the tubular and vesicular vacuolar-network. Furthermore, the loss of intercalary
septation in ascogonia suggests that PRO22 functions during the initiation of sexual
development.