The fungal opsin gene nop-1 is negatively-regulated by a component of the blue light sensing pathway and influences conidiation-specific gene expression in Neurospora crassa

We previously demonstrated that the nop-1 gene encodes a putative green-light opsin photoreceptor that is highly expressed in cultures that support asexual sporulation (conidiation) in Neurospora crassa. In this study, we demonstrate that nop-1 is a late-stage conidiation gene, through analysis of nop-1 transcript levels in wildtype strains and mutants blocked at various stages of conidiation. nop-1 message amounts are similar with constant illumination or darkness during conidiation, consistent with developmental, but not light, regulation of nop-1 expression. Furthermore, photoinduction experiments using wild type and mutants defective in components of the blue light sensing pathway (wc-1 and wc-2) indicate that nop-1 mRNA levels are not appreciably affected by brief light exposure during conidiation. Surprisingly, nop-1 message amounts are greatly elevated in wc-2 mutants in light or dark, suggesting that the wc-2 gene product regulates nop-1 expression in a light-independent manner. Analysis of expression patterns for al-2, con-10 and con-13, genes regulated by conidiation and/or blue light, showed that nop-1 has significant and reproducible effects on all three genes during various stages of conidiation. The results suggest that NOP-1 directly or indirectly modulates carotenogenesis and repression of conidiation-specific gene expression in N. crassa.