Comparisons of Two Wildtype A Mating Type Alleles and Derived Self-Compatible Mutants in the Basidiomycete Coprinopsis cinerea

摘要

The A mating type locus in Coprinopsis cinerea controls defined steps in the formation and maintenance of a dikaryotic mycelium after mating of two compatible monokaryons.In addition,fruiting body formation on the established dikaryon is regulated by the A genes.The AA mating type locus has multiple alleles.The estimated total number of A alleles for C.cinerea in nature is 160.The AA locus is about 20 kb in size and has a complex structure.Usually,an A allele has three paralogous pairs of divergently transcribed genes that encode two distinct types of homeodomain transcription factors (termed HD 1 and HD2).Different A alleles distinguish by different alleles in these gene pairs.For regulation of sexual development,heterodimerization between HD1 and HD2 proteins coming from allelic gene pairs is required.In some A loci as found in nature,some alleles of gene pairs are not complete or one of the two paired genes has been made inactive.However,functional redundancy allows the system to still work as long as an HD1 gene in one and an HD2 gene in the other allele of one gene pair are operative.Here,we present the structures of two completely sequenced A loci,A42 and A43.The loci differ in the number of potential gene pairs (five versus three).Different genes in these AA mating types have been duplicated,lost or inactivated in evolution.Furthermore to wildtype A alleles,rare self-compatible mutants with defects in the AA locus are known that can carry out sexual reproduction without mating with another compatible strain.In two of such mutant A alleles,an HD1 and an HD2 gene have been fused into a single transcribed gene.The encoded fusion products can take over the regulatory functions that are normally accomplished by heterodimers formed by HD1 and HD2 proteins originating from different nuclei.Here,we present the structure of two different HD1-HD2 fusion genes.Comparison between the encoded fusion proteins indicates that the HD2 homeodomain and NLSs (nuclear localization signals) from the HD 1 protein are likely essential for the function of the fusion proteins.Other domains required for function in the wild type proteins such as for HD1-HD2 heterodimerization are dispensable for fusion proteins that mediate a self-compatible phenotype.