International Symposium on Cereal Leaf Blights 2019 | University College Dublin, Ireland | 22-24 May 2019

The role of vegetative hyphal fusions in Zymoseptoria tritici


Carolina S Francisco*
Plant Pathology Group, Institute of Integrative Biology, ETH Zürich, Switzerland

Maria M Zwyssig
Plant Pathology Group, Institute of Integrative Biology, ETH Zürich, Switzerland

Marcello Zala
Plant Pathology Group, Institute of Integrative Biology, ETH Zürich, Switzerland

Javier Palma-Guerrero
Plant Pathology Group, Institute of Integrative Biology, ETH Zürich, Switzerland


Oral Presentation
Pathogen Functional Genetics and Genomics

Moore Auditorium, UCD O'Brien centre for Science
23 May 2019, 09:40

View this abstract online by visting isclb2019.com/see/ABS50065

Vegetative hyphal fusions (VHFs) allow the formation of interconnected hyphal networks in filamentous fungi, which favors the distribution of nutrients and signals within the fungal colony. Contrary to cell fusions during sexual reproduction that requires different mating types, VHFs occur between genetically identical individuals. The best characterized gene required for VHFs is the soft (So) gene, which was first identified in the fungus Neurospora crassa and its deletion results in a complete absence of VHFs and shortened aerial hyphae. So is highly conserved among Ascomycetes fungi, and it has been shown to be essential for hyphal fusion and pathogenicity in Fusarium oxysporum and Alternaria brassicicola. However, the connection between hyphal fusion and pathogenicity is still unclear. Here we have investigated VHFs and their role in virulence in the wheat pathogen Zymoseptoria tritici. We used strains expressing different cytoplasmic fluorescent proteins to detect cytoplasm mixing after cell fusion events, and we found that hyphal fusions are frequent in this pathogen both in vitro and in planta. We identified the So gene in the Z. tritici genome and obtained a deletion mutant (ΔZtSo). ΔZtSo shows a complete absence of hyphal fusions, but the fusion ability is recovered when the mutant is complemented with the ZtSo gene. The disease progression in ΔZtSo is similar to wild type, but pycnidia are completely absent in the mutant. Despite the absence of pycnidia, confocal microscopy and qPCR measurements during leave infection showed an earlier increase of fungal biomass in ΔZtSo. In conclusion, we show that hyphal fusions are not required for host invasion and host damage in Z. tritici, but they are essential for pycnidia formation.