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Eukaryotic Cell doi:10.1128/EC.00427-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Neurospora crassa heat shock factor-1 is an essential gene; a second heat shock factor-like gene, hsf2, is required for asexual spore formation

Faculty of Life Sciences, University of Manchester, M13 9PT, U. K.

^* To whom correspondence should be addressed. Email: susan.k.crosthwaite{at}manchester.ac.uk.

	Abstract

Appropriate responses of organisms to heat stress are essential for their survival. In eukaryotes adaptation to high temperatures is mediated by heat shock factors (HSF). HSFs regulate the expression of heat shock proteins that function as molecular chaperones, assisting in protein folding and stability. In many model organisms, a great deal is known about the products of hsf genes. An important exception is the filamentous fungus and model eukaryote Neurospora crassa. Here we show that two Neurospora crassa genes whose protein products share similarity to known heat shock transcription factors play different biological roles. We report that heat shock factor 1 (hsf1) is an essential gene and that hsf2 is required for asexual development. Conidiation may be blocked in the hsf2^KO because HSF2 is an integral element of the conidiation pathway or because it affects the availability of protein chaperones. We report that genes expressed during conidiation, for example fluffy, conidiation-10 and repressor of conidiation-1 show wild-type levels of expression in a hsf2^KO strain. However, consistent with the lack of macroconidia development, levels of eas are much reduced. Cultures of hsf2^KO along with two other aconidial strains, fluffy and aconidial-2, took longer than wild-type to recover from heat shock. Altered expression profiles of hsp90 and a putative hsp90-associated protein in hsf2^KO after exposure to heat shock may in part account for its reduced ability to cope with heat stress.