The frost gene of Neurospora crassa is a homolog of yeast cdc1 and affects hyphal branching via manganese homeostasis

The Neurospora crassa mutant frost has a hyperbranching phenotype that can be corrected by adding Ca(2+), suggesting that characterization of this gene might clarify the mechanism of Ca(2+)-dependent tip growth. The wild-type allele was cloned by sib selection using protoplasts from arthroconidia. RFLP analysis revealed that the cloned DNA fragment mapped to the fr locus. The nucleotide sequence of genomic and cDNA was determined. The deduced amino acid sequence showed homology to the Saccharomyces cerevisiae CDC1 protein, implicated in manganese homeostasis. The fr mutant was sensitive to Mn(2+), and a revertant allele whose product differs by one amino acid was tolerant to Mn(2+). Mn(2+) depletion induced the wild-type strain to hyperbranch, resulting in a morphology similar to that of fr. The fr mutant was also sensitive to calcineurin inhibitors. These results suggest that fr is involved in Mn(2+) homeostasis and point to a role for Mn(2+) in Neurospora branching.