Role of the XylA gene, encoding a cell wall degrading enzyme, during common wheat, durum wheat and barley colonization by Fusarium graminearum.

Fusarium graminearum is the main causal agent of fusarium head blight (FHB) of wheat and barley. This filamentous fungus is able to produce hydrolytic enzymes, such as xylanases, that cause cell wall degradation, permitting host colonization. This study investigated the role of the F. graminearum XylA (FGSG_10999) gene during infection, using a knockout mutant in strain CS3005. Assays were carried out on common wheat, durum wheat and barley to compare virulence of a XylA knockout to that of wild type strain. These assays were conducted on wheat and barley seedling roots, seedling stem bases and heads. Furthermore, additional in vitro experiments were conducted to investigate the role of XylA gene in the utilisation of D-xylose, the main component of cereals cell wall. In planta assays showed the importance of XylA gene for F. graminearum virulence towards its main hosts. A positive correlation between symptom incidence and fungal biomass development was also observed for both the wild type and the knockout strains. Finally, gene expression studies performed in a liquid medium enriched with D-xylose, a known xylanase inducer in other fungi, showed that the absence of the gene in the FGSG_10999 locus was not compensated by two other F. graminearum xylanase encoding genes analysed (loci FGSG_06445 and FGSG_11478).