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Eukaryotic Cell, May 2009, p. 738-746, Vol. 8, No. 5
1535-9778/09/$08.00+0     doi:10.1128/EC.00368-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Differential Roles of the ChiB Chitinase in Autolysis and Cell Death of Aspergillus nidulans{triangledown}

Kwang-Soo Shin,1 Nak-Jung Kwon,2 Young Hwan Kim,3 Hee-Soo Park,2 Gi-Seok Kwon,4 and Jae-Hyuk Yu2*

Department of Microbiology and Biotechnology, Daejeon University, Daejeon, Republic of Korea,1 Departments of Bacteriology and Genetics, University of Wisconsin, Madison, Wisconsin,2 Mass Spectrometry Research Center/Mass Spectrometry Team, Korea Basic Science Institute, Daejeon, Republic of Korea,3 School of Bioresource Sciences, Andong National University, Andong, Republic of Korea4

Received 17 November 2008/ Accepted 18 February 2009

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 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 using a set of critical mutants. Determination of mycelial mass revealed that, while the flbA deletion ({Delta}flbA) mutant autolyzed completely after a 3-day incubation, the {Delta}flbA {Delta}chiB double mutant escaped from hyphal disintegration. These results indicate that ChiB is necessary for the {Delta}flbA-induced autolysis. However, importantly, both {Delta}flbA and {Delta}flbA {Delta}chiB strains displayed dramatically reduced cell viability compared to the wild type. These imply that ChiB is dispensable for cell death and that autolysis and cell death are separate processes. Liquid chromatography-tandem mass spectrometry analyses of the proteins that accumulate at high levels in the {Delta}flbA and {Delta}flbA {Delta}chiB mutants identify chitinase (ChiB), dipeptidyl peptidase V (DppV), O-glycosyl compound hydrolase, β-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.

* Corresponding author. Mailing address: Departments of Bacteriology and Genetics, University of Wisconsin, Madison, WI 53706. Phone: (608) 262-4696. Fax: (608) 262-9865. E-mail: jyu1{at}wisc.edu

{triangledown} Published ahead of print on 13 March 2009.

Eukaryotic Cell, May 2009, p. 738-746, Vol. 8, No. 5
1535-9778/09/$08.00+0     doi:10.1128/EC.00368-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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