J. Basic Microbiol. 46 (2006) 6, 495 – 503 DOI: 10.1002/jobm.200610174 © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 0233-111X/06/0612-0495 (Department of Microbiology and Biotechnology, Faculty of Science, University of Debrecen, H-4010 Debrecen, P.O. Box: 63, Hungary) Effects of mutations in the GanB/RgsA G protein mediated signalling on the autolysis of Aspergillus nidulans ZSOLT MOLNÁR, TAMÁS EMRI*, ERZSÉBET ZAVACZKI, TÜNDE PUSZTAHELYI and ISTVÁN PÓCSI (Received 08 March 2006/Returned for modification 27 March 2006/Accepted 28 April 2006) Physiological changes taking place in carbon-starved, autolysing cultures of Aspergillus (Emericella) nidulans strains with mutations in the GanB/RgsA heterotrimeric G protein signalling pathway were studied and compared. Deletion of the ganB, rgsA or both genes did not alter markedly either the autolytic loss of biomass or the extracellular chitinase production. However, they caused a significant decrease in the proteinase formation, which was detected by measuring both extracellular enzyme activity and the transcription of the prtA gene. The deletion mutants also showed significantly higher specific γ-glutamyltranspeptidase activities than the control strain. Deletion of the rgsA gene affected the glutathione peroxidase and catalase formation, as well as the peroxide content of the cells. The concomitant initiations of cell death and developmental genomic programmes may be interconnected via heterotrimeric G-protein signalling and subsequent changes in intracellular ROS levels in ageing A. nidulans. G protein mediated signalling pathways have a crucial role in the regulation of asexual sporulation, vegetative growth and sense of various extracellular signals in Aspergillus nidulans (ADAMS et al. 1998, CHANG et al. 2004). In the A. nidulans genome nine putative GPCR coding genes (gprA–L) were identified (HAN et al. 2004, SEO et al. 2004). The suit- able G protein pairs of the GPCRs have not been identified yet despite of that in A. nidulans there are three known G protein α subunits (FadA, GanA-B) (LEE and ADAMS 1994, YU et al. 1996, CHANG et al. 2004, HAN et al. 2004, LAFON et al. 2005). Heterotrimeric G pro- teins are controlled by RGS (regulator of G protein signalling) proteins, of which four (flbA, rgsA-C) have been found by this time (LEE and ADAMS 1994, YU et al. 1996, 1999, WIESER et al. 1997, HAN et al. 2004). The RGS pair of FadA is FlbA (LEE et al. 1994, YU et al. 1996, 1999) while GanB is controlled by RgsA (HAN et al. 2004). Since there is only one Gβ and Gγ subunit in the A. nidulans genome database (CHANG et al. 2004) the FadA/FlbA and GanB/RgsA pathways seem to share the same Gβγ subunit. The FadA/FlbA signalling maintains vegetative growth and represses asexual and sexual development as well as sterigmatocystin production (LEE et al. 1994, YU et al. 1996, 1999, ADAMS et al. 1998, SEO et al. 2005). The GanB/RgsA signalling plays a positive role during germination of conidia and ascospores through carbon source sensing and negatively regulates asexual sporulation (CHANG et al. 2004, HAN et al. 2004, LAFON et al. 2005). It also controls pigment synthesis and some aspects of stress responses in A. nidulans (HAN et al. 2004). Here we present the role of GanB/RgsA signalling (CHANG et al. 2004, HAN et al. 2004, LAFON et al. 2005) in the carbon starvation induced stress response of Aspergillus nidulans. * Corresponding author: Prof. T. EMRI; e-mail: emri@freemail.hu