FpCBS Affects a Diverse Range of Functions of Fusarium pseudograminearum Impacting Its Virulence to Wheat

A cystathionine β-synthase (CBS) gene, FpCBS, of the wheat crown rot pathogen, Fusarium pseudograminearum, was identified. FpCBS was highly expressed during conidiation and the early phases of infection. Compared to the wild-type and FpCBS complemented strains, the FpCBS deletion strain had a similar hyphal morphology and growth rate but reduced conidiation. In culture, the FpCBS deletion strain showed broad-scale changes with a decrease in H₂S levels, changes in sulphur-containing amino acids and 1207 differentially expressed proteins. The deletion strain also showed reduced deoxynivalenol (DON) production, cellophane penetration ability, antioxidant capacity, as well as increased hyphal iron levels, sensitivity to H₂O₂ and lipid peroxidation. During infection, the ΔFpcbs strain showed diminished virulence to wheat with fewer penetration structures, and there was a stronger host defence response with wheat epidermal cells having thickened walls and greater reactive oxygen species accumulation. Transcriptomic analysis of infected leaves showed 1954 differentially expressed genes in the FpCBS deletion strain compared to the wild-type strain. This included genes for sulphur metabolism, antioxidative defence, plant cell wall-degrading enzymes and trichothecene production. FpCBS not only plays a pivotal role in sulphur metabolism and H₂S production, but it is also important for a broad range of fungal functions, including iron homoeostasis, mycotoxin production and development (conidiation and penetration structures). These factors may all contribute to varying extents to the significant decrease in virulence of the FpCBS deletion strain. The findings have shown that FpCBS is important for much more than sulphur metabolism and H₂S synthesis. However, its role in virulence highlights its potential as a novel target for developing strategies to control wheat crown rot.