The function of 1,3-β-glucan in Zymoseptoria tritici and the control of Septoria tritici blotch

Zymoseptoria tritici (Z. tritici) is a global wheat pathogen and the causative agent of
Septoria tritici blotch (STB), causing crop losses of up to 50% in high-disease
pressure years, with extreme economic consequences. Due to emerging resistance
to current fungicides, new targets for future fungicide development is essential. The
fungal cell wall is a protective and dynamic outer layer to the cell, obtaining a crucial
role in the survival and virulence of the cell, and presents itself as a promising target
for fungicide development.

This thesis investigates the roles of 1,3-β-glucan, a key component of the fungal cell
wall, in Z. tritici growth and pathogenicity and assesses its potential as a fungicide
target. Through the generation of 1,3-β-glucan mutants deficient in 1,3-β-glucan
biosynthesis, the morphology, colony phenotypes and virulence of these mutants are
explored. The results demonstrate that 1,3-β-glucan is crucial for hyphal formation in
liquid culture, and melanisation on solid-media. The 1,3-β-glucan deficient mutants
also displayed reduced virulence while cryogenic scanning electron microscopy
revealed that this is due to impaired spore attachment, possibly due to changes in
the cell wall structure. The use of atomic force microscopy to directly compare Z.
tritici cell wall structure at high resolution between mutants deficient in 1,3-β-glucan
and the wild-type (IPO323) confirms that disruption of 1,3-β-glucan significantly
alters cell wall structure and is, therefore, a promising target for future fungicides. As
a promising target, in this thesis, a plate-based assay to measure 1,3-β-glucan
biosynthesis has been developed. This will aid in the establishment of a compound
screening platform for fungicide development.