Importance of endo-xylanase encoding genes in Fusarium graminearum enzymatic activity and pathogenicity

Fusarium graminearum is a plant pathogen responsible for the Fusarium head blight disease in cereals, which reduces grain yield and quality. During the infection process, the fungus produces several cell wall-degrading enzymes to penetrate the host tissues. Among these enzymes, xylanases are crucial for the degradation of xylan, a major component of monocot plant cell walls. In this study, we focused on FGSG_03624 and FGSG_10999, two endo-xylanase encoding genes highly expressed during wheat spike infection, which were knocked-out by inserting an antibiotic resistance gene. Pathogenicity assays on Triticum aestivum spikes and soybean seeds, performed with both single and double mutants, highlighted that only the deletion of FGSG_10999 significantly reduces fungal virulence on both plant hosts compared to the wild-type and KO_03624 strains. However, the double knock-out mutant exhibited virulence like the single FGSG_03624 mutant. Additionally, we compared the xylanase, cellulase, and pectinase activities produced by the mutant strains with those of the wild-type and we evaluated the genetic expression of other endo-xylanase encoding genes during wheat spike infection at three days post-inoculation to assess any compensatory effects resulting from the absence of the two knocked-out genes. Results showed that both the single KO_10999 strain and the double knockout mutant, were affected in the secretion of total xylanase activity. Expression analysis highlighted that two endoxylanase genes are over-expressed in the mutants with the FGSG_10999 gene deleted. Further experiments are needed to clarify the lower virulence of the single FGSG_10999 mutant compared to the double mutant.