Developmental and Photoregulation of Three Neurospora crassa Carotenogenic Genes during Conidiation Induced by Desiccation.

Neurospora crassa asexual sporulation (conidiation) is induced by different cues including desiccating aerial environments. Three of the genes that are expressed during this developmental pathway are the albino (al) genes, which encode carotenoid biosynthetic enzymes. If conidiation is induced by nutrient deprivation in liquid culture, two overlapping al-3 mRNAs, al-3 (m) and al-3 (c), are expressed (Arpaia et al., 1995, Dev. Biol. 170, 620-635). Here we quantitate accumulation of each of the four albino gene messages, al-1, al-2, al-3 (m), and al-3 (c), in conidiating wild-type cultures and in cultures of two mutants defective in photoinduced carotenogenesis, wc-1 and wc-2. Of the four albino gene transcripts, only al-1 expression is developmentally regulated in wild-type cultures conidiating in darkness. Expression of all four albino gene transcripts is developmentally regulated in conidiating wc-1 or wc-2 cultures. Unlike other albino gene transcripts, expression of al-3 (c) is photoregulated only early in conidiation. The fld and fl mutants are defective in conidiation with development halting at distinct early stages of spore formation. In desiccated fld and fl cultures al-1, al-2, and al-3 (m) transcript accumulation is observed to peak early and then decline, while al-3 (c) transcript accumulation increases with time.