DIFFERENTIAL EXPRESSION OF GLUCOSE-REGULATED (GRP78) AND HEAT-SHOCK-INDUCIBLE (HSP70) GENES DURING ASEXUAL DEVELOPMENT OF NEUROSPORA-CRASSA

The expression of a glucose-regulated gene (grp78) changes significant ly during the vegetative life cycle of Neurospora crassa: the amounts of grp78 mRNA are low in dormant conidia, increase during germination and exponential growth, decline in young aerial hyphae and reach a max imum in late (15-18 h) aerial hyphae. Heat shock (30 min at 45 degrees C) elevated the mRNA level of this gene especially in early aerial hy phae, whereas no increase above the high constitutive amount was found after heat treatment of late aerial hyphae. The expression of the ind ucible hsp70 gene after heat shock also varied with the state of devel opment and showed the highest inducibility in late aerial hyphae. Surf ace mycelium, from which aerial hyphae emerge, showed a similar increa se in the amounts of both mRNA species. A developmental mutant (acon-2 ), which is defective in minor constriction budding of aerial hyphae, showed lower levels of con-2 mRNA as well as of grp78 and hsp70 mRNA ( after heat shock) in late aerial hyphae. The acon-2 mutant did not for m conidia at this stage. It is concluded that the high constitutive an d inducible expression of stress genes in late aerial hyphae is due to a developmental activation of their transcription or, alternatively. to a lower degradation rate of their mRNA during this stage.