Calcineurin subunit B is required for normal vegetative growth in Neurospora crassa

A series of Neurospora crassa mutants 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 regulated ccg-1 gene is constitutively expressed in these cells, suggesting that they have entered the conidial developmental program. The insertionally disrupted gene cnb-1 was 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 in N. crassa and suggest that the cnb-1 mutant is unable to repress entry into the asexual developmental program. The results suggest that Ca²⁺ may play an important role in regulating fungal morphology.