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Eukaryotic Cell, December 2008, p. 2113-2122, Vol. 7, No. 12
1535-9778/08/$08.00+0     doi:10.1128/EC.00466-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Mitogen-Activated Protein Kinase Cascade Required for Regulation of Development and Secondary Metabolism in Neurospora crassa{triangledown}

Gyungsoon Park,1 Songqin Pan,2 and Katherine A. Borkovich1,2*

Department of Plant Pathology and Microbiology, 1415 Boyce Hall,1 Institute for Integrative Genome Biology, University of California, Riverside, 900 University Avenue, Riverside, California 925212

Received 31 December 2007/ Accepted 26 September 2008

Mitogen-activated protein kinase (MAPK) signaling cascades are composed of MAPK kinase kinases (MAPKKKs), MAPK kinases (MAPKKs), and MAPKs. In this study, we characterize components of a MAPK cascade in Neurospora crassa (mik-1, MAPKKK; mek-1, MAPKK; and mak-1, MAPK) homologous to that controlling cell wall integrity in Saccharomyces cerevisiae. Growth of basal hyphae is significantly reduced in mik-1, mek-1, and mak-1 deletion mutants on solid medium. All three mutants formed short aerial hyphae and the formation of asexual macroconidia was reduced in {Delta}mik-1 mutants and almost abolished in {Delta}mek-1 and {Delta}mak-1 strains. In contrast, the normally rare asexual spores, arthroconidia, were abundant in cultures of the three mutants. {Delta}mik-1, {Delta}mek-1, and {Delta}mak-1 mutants were unable to form protoperithecia or perithecia when used as females in a sexual cross. The MAK-1 MAPK was not phosphorylated in {Delta}mik-1 and {Delta}mek-1 mutants, consistent with the involvement of MIK-1, MEK-1, and MAK-1 in the same signaling cascade. Interestingly, we observed increased levels of mRNA and protein for tyrosinase in the mutants under nitrogen starvation, a condition favoring sexual differentiation. Tyrosinase is an enzyme that catalyzes production of the secondary metabolite L-DOPA melanin. These results implicate the MAK-1 pathway in regulation of development and secondary metabolism in filamentous fungi.

* Corresponding author. Mailing address: Department of Plant Pathology and Microbiology, 1415 Boyce Hall, University of California, Riverside, 900 University Avenue, Riverside, CA 92521. Phone: (951) 827-2753. Fax: (951) 827-4294. E-mail: Katherine.Borkovich{at}ucr.edu

{triangledown} Published ahead of print on 10 October 2008.

Eukaryotic Cell, December 2008, p. 2113-2122, Vol. 7, No. 12
1535-9778/08/$08.00+0     doi:10.1128/EC.00466-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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