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Eukaryotic Cell, August 2005, p. 1465-1476, Vol. 4, No. 8
1535-9778/05/$08.00+0     doi:10.1128/EC.4.8.1465-1476.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

The pkaB Gene Encoding the Secondary Protein Kinase A Catalytic Subunit Has a Synthetic Lethal Interaction with pkaA and Plays Overlapping and Opposite Roles in Aspergillus nidulans

Min Ni,^1,3 Sara Rierson,^1, Jeong-Ah Seo,¹ and Jae-Hyuk Yu^1,2*

Department of Food Microbiology and Toxicology & Food Research Institute,¹ Molecular and Environmental Toxicology Center,² Department of Genetics, University of Wisconsin—Madison, 1925 Willow Drive, Madison, Wisconsin 53706³

Received 12 April 2005/ Accepted 8 June 2005

Filamentous fungal genomes contain two distantly related cyclic AMP-dependent protein kinase A catalytic subunits (PKAs), but only one PKA is found to play a principal role. In Aspergillus nidulans, PkaA is the primary PKA that positively functions in vegetative growth and spore germination but negatively controls asexual sporulation and production of the mycotoxin sterigmatocystin. In this report, we present the identification and characterization of pkaB, encoding the secondary PKA in A. nidulans. Although deletion of pkaB alone does not cause any apparent phenotypic changes, the absence of both pkaB and pkaA is lethal, indicating that PkaB and PkaA are essential for viability of A. nidulans. Overexpression of pkaB enhances hyphal proliferation and rescues the growth defects caused by pkaA, indicating that PkaB plays a role in vegetative growth signaling. However, unlike pkaA, deletion of pkaB does not suppress the fluffy-autolytic phenotype resulting from flbA. While upregulation of pkaB rescues the defects of spore germination resulting from pkaA in the presence of glucose, overexpression of pkaB delays spore germination. Furthermore, upregulation of pkaB completely abolishes spore germination on medium lacking a carbon source. In addition, upregulation of pkaB enhances the level of submerged sporulation caused by pkaA and reduces hyphal tolerance to oxidative stress. In conclusion, PkaB is the secondary PKA that has a synthetic lethal interaction with PkaA, and it plays an overlapping role in vegetative growth and spore germination in the presence of glucose but an opposite role in regulating asexual sporulation, germination in the absence of a carbon source, and oxidative stress responses in A. nidulans.

Present address: USDA-ARS, U.S. Dairy Forage Research Center, 1925 Linden Drive West, Madison, WI 53706.

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