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.