Differential stress gene expression during the development of Neurospora crassa and other fungi.

Stress genes are differentially expressed during the development of Neurospora crassa and other fungi. Large amounts of constitutive heat shock protein 70 (HSC70) are found in dormant conidia of N. crassa, whereas little mRNA of the related glucose-regulated protein (grp78) is detected. It is, however, not generally clear whether heat shock protein or mRNA is preferentially stored in dormant spores. Germinating spores of N. crassa increase the level of grp mRNA. During this developmental stage, the induction of inducible heat shock protein (hsp) genes can be elicited by heat shock only at certain times after the beginning of germination. Exponential growth (proliferation) is paralleled by increased levels of HSCs. The stationary state is characterized by decreased levels of some HSCs and increased levels of others. Conidiation in N. crassa is accompanied by a strong enhancement of the synthesis and levels of HSCs but also of HSPs after heat shock. This increase may serve a need for additional rounds of replication, for the expression and transport of sporulation-specific proteins or for stabilization of macromolecules in the spores and their preservation for germination. The control mechanisms involved in the differential expression of hsc genes are currently not known.