Members of Glycosyl-Hydrolase Family 17 of A. fumigatus Differentially Affect Morphogenesis

Cell wall biosynthesis and remodeling are essential for fungal growth and development. In the fungal pathogen Aspergillus fumigatus, the β(1,3)glucan is the major cell wall polysaccharide. This polymer is synthesized at the plasma membrane by a transmembrane complex, then released into the parietal space to be remodeled by enzymes, and finally incorporated into the pre-existing cell wall. In the Glycosyl-Hydrolases family 17 (GH17) of A. fumigatus, two β(1,3)glucanosyltransferases, Bgt1p and Bgt2p, have been previously characterized. Disruption of BGT1 and BGT2 did not result in a phenotype, but sequence comparison and hydrophobic cluster analysis showed that three other genes in A. fumigatus belong to the GH17 family, SCW4, SCW11, and BGT3. In constrast to Δbgt1bgt2 mutants, single and multiple deletion of SCW4, SCW11, and BGT3 showed a decrease in conidiation associated with a higher conidial mortality and an abnormal conidial shape. Moreover, mycelium was also affected with a slower growth, stronger sensitivity to cell wall disturbing agents, and altered cell wall composition. Finally, the synthetic interactions between Bgt1p, Bgt2p, and the three other members, which support a functional cooperation in cell-wall assembly, were analyzed. Our data suggest that Scw4p, Scw11p, and Bgt3p are essential for cell wall integrity and might have antagonistic and distinct functions to Bgt1p and Bgt2p.