Calcineurin Subunit B Is Required for Normal Vegetative Growth inNeurospora crassa

A series ofNeurospora crassamutants affected in the ability to regulate entry into conidiation (an asexual developmental program) were isolated by using an insertional mutagenesis procedure followed by a screening protocol. One of the mutants isolated by this approach consisted entirely of cells with an abnormal morphology. The mutant produces chains of swollen septated cells. The developmentally regulatedccg-1gene is constitutively expressed in these cells, suggesting that they have entered the conidial developmental program. The insertionally disrupted genecnb-1was isolated by plasmid rescue and found to encode calcineurin B, the regulatory subunit of the Ca²⁺and calmodulin-dependent protein phosphatase calcineurin. The data demonstrate that calcineurin B is required for normal vegetative growth inN. crassaand suggest that thecnb-1mutant is unable to repress entry into the asexual developmental program. The results suggest that Ca²⁺may play an important role in regulating fungal morphology.