Article,
Differential Roles of the ChiB Chitinase in Autolysis and Cell Death of Aspergillus nidulans
Eukaryot Cell, (March 2009)
DOI: 10.1128/EC.00368-08
Abstract
Autolysis is a natural event that occurs in most filamentous fungi. Such self-degradation of fungal cells becomes a predominant phenomenon in the absence of the regulator of G protein signaling (RGS) FlbA in Aspergillus nidulans. Among a number of potential hydrolytic enzymes in the A. nidulans genome, the secreted endochitinase ChiB was shown to play a major role in autolysis. In this report, we investigate the roles of ChiB in fungal autolysis and cell death processes through genetic, biochemical and cellular analyses employing a set of critical mutants. Determination of mycelial mass revealed that, while the flbA deletion (DeltaflbA) mutant autolyzed completely after 3-d incubation, the DeltaflbA DeltachiB double mutant escaped from hyphal disintegration. These results indicate that ChiB is necessary for the DeltaflbA-induced autolysis. However, importantly, both DeltaflbA and DeltaflbA DeltachiB strains displayed dramatically reduced cell viability compared to wild type. These imply that ChiB is dispensable for cell death and that autolysis and cell death are separate processes. LC-MS-MS analyses of the proteins that accumulate at high levels in the DeltaflbA and DeltaflbA DeltachiB mutants identify chitinase (ChiB), dipeptidyl peptidase V (DppV), O-glycosyl compound hydrolase, beta-N-acetylhexosaminidase (NagA) and myo-inositol-1-phosphate synthase (InoB). Functional characterization of these four genes reveals that the deletion of nagA results in reduced cell death. A working model bridging G protein signaling and players in autolysis/cell death is proposed.
