In vitro and in vivo characterization of Fusarium graminearum single and double knock-out mutants of genes encoding endo-β-1,4-xylanases.

Fusarium graminearum is a fungal plant pathogen known for being the causal agent of the Fusarium Head Blight (FHB) disease of cereal crops. This fungus usually attacks wheat spikes at flowering, and it is one of the main causes of reduction in yield and crop quality due to the contamination of grains with mycotoxins such as deoxynivalenol (DON). During the infection process, F. graminearum has been shown to degrade the wheat cell wall through the activity of several cell wall degrading enzymes (CWDEs). Indeed, the plant cell wall is mainly composed of polysaccharides such as cellulose, pectin and hemicelluloses and it acts as a first barrier against fungal pathogens. Among hemicelluloses component of wheat cell walls, xylan is one of its major components. Xylan can be degraded by endo-xylanases which are a class of CWDEs. During wheat infection, F. graminearum expresses multiple genes encoding for xylanase activity, which two of them are highly expressed, namely FGSG_03624 and FGSG_10999. Single and double knock-out mutants for these genes were obtained in order to characterize the xylanase activity, allowing mutants to grown in xylan containing medium. The virulence of the mutants was also tested on wheat seedlings to characterize the xylanase role in wheat infection. The disruption of the FGSG_10999 and FGSG_03624 genes lead to have a double mutant that showed a reduction in xylanase activity compared to the wild type PH1 strain thus confirming the involvement of these two xylanases in xylan degradation. However, the virulence and fungal growth of this double mutant is not affected despite having a significant reduction in total xylanase activity