Neurospora crassa heat shock factor 1 Is an Essential Gene; a Second Heat Shock Factor-Like Gene, hsf2 , Is Required for Asexual Spore Formation

Abstract

Appropriate responses of organisms to heat stress are essential for their survival. In eukaryotes, adaptation to high temperatures is mediated by heat shock transcription factors (HSFs). HSFs regulate the expression of heat shock proteins, which 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 HSFs 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 knockout (hsf2 KO ) strain 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 macroconidium development, levels of eas are much reduced. Cultures of the hsf2 KO strain along with two other aconidial strains, the fluffy and aconidial-2 strains, took longer than the wild type to recover from heat shock. Altered expression profiles of hsp90 and a putative hsp90-associated protein in the hsf2 KO strain after exposure to heat shock may in part account for its reduced ability to cope with heat stress.

Transcription of the Neurospora crassa 70-kDa class heat shock protein genes is modulated in response to extracellular pH changes

“…Data are average values ± standard deviation (SD) obtained from two independent experiments gene might not be under the direct control of PACC. Eukaryotic heat shock factors (HSFs) regulate constitutive and stress-inducible transcription of various genes, including the hsp genes and, thereby, play a central role in the regulation of numerous cellular reprogramming events (Hahn et al 2006;Hashikawa et al 2007;Sakurai and Takemori 2007;Thompson et al 2008). HSF proteins recognize continuous and discontinuous repeats of 5′-nGAAn-3′ in target genes; these repeats are present in the sequences upstream of the hsp70-1, hsp70-2, and hsp70-3 genes.…”

Transcription Factors in Light and Circadian Clock Signaling Networks Revealed by Genomewide Mapping of Direct Targets for Neurospora White Collar Complex

“…Developmental stages that have been associated with light regulation, i.e., asexual sporulation (conidiation) and sexual development, are represented by nine TFs whose mutation results in developmental phenotypes (hsf-2, adv-1, sub-1, sah-1, sah-2, bek-1, vad-2, csp-1, and ghh) (11,46). All nine genes are induced by light, and this response is abolished in a wc-2 deletion strain ( [35]).…”

Heat Shock Protein 90 Is Required for Conidiation and Cell Wall Integrity in Aspergillus fumigatus

“…Deletion of the heat shock transcription factor hsf2 has been associated with an altered expression profile of hsp90 and an aconidial phenotype in N. crassa (37). In S. cerevisiae, compromising Hsp90 function also resulted in defective spore formation (36).…”