Molecular characterization of tol, a mediator of mating-type-associated vegetative incompatibility in Neurospora crassa

• Published in: Genetics (Austin) 1999-02, Vol.151 (2), p.545-555
• Main Authors: Shiu, P.K.T, Glass, N.L
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; amino acid sequences; Amino acids; Base Sequence; cell fusion; Cells; chromosome mapping; chromosomes; deletions; Fungal Proteins - chemistry; Fungal Proteins - genetics; genbank/af085183; gene expression; Gene Expression Regulation, Fungal; Genes, Fungal; Genes, Mating Type, Fungal; genetic complementation; genetic markers; Genetics; growth; heterokaryosis; hyphae; incompatibility; introns; Leucine; loci; messenger RNA; Molecular Sequence Data; mutants; mutation; Neurospora crassa; Neurospora crassa - genetics; Neurospora crassa - growth & development; nucleotide sequences; open reading frames; phenotype; polypeptides; Protein Conformation; recessive genes; Reproduction; restriction fragment length polymorphism; Ribonucleic acid; RNA; tol locus; vegetative growth
• ISSN: 0016-6731; 1943-2631; 1943-2631
• DOI: 10.1093/genetics/151.2.545

The mating-type locus in the haploid filamentous fungus, Neurospora crassa, controls mating and sexual development. The fusion of reproductive structures of opposite mating type, A and a, is required to initiate sexual reproduction. However, the fusion of hyphae of opposite mating type during vegetative growth results in growth inhibition and cell death, a process that is mediated by the tol locus. Mutations in tol are recessive and suppress mating-type-associated heterokaryon incompatibility. In this study, we describe the cloning and characterization of tol. The tol gene encodes a putative 1011-amino-acid polypeptide with a coiled-coil domain and a leucine-rich repeat. Both regions are required for tol activity. Repeat-induced point mutations in tol result in mutants that are wild type during vegetative growth and sexual reproduction, but that allow opposite mating-type individuals to form a vigorous heterokaryon. Transcript analyses show that tol mRNA is present during vegetative growth but absent during a cross. These data suggest that tol transcription is repressed to allow the coexistence of opposite mating-type nuclei during the sexual reproductive phase. tol is expressed in a mat A, mat a, A/a partial diploid and in a mating-type deletion strain, indicating that MAT A-1 and MAT a-1 are not absolutely required for transcription or repression of tol. These data suggest that TOL may rather interact with MAT A-1 and/or MAT a-1 (or downstream products) to form a death-triggering complex.