Abstract
Higher fungi, which comprise ascomycetes and basidiomycetes, play major roles in the biosphere. Their evolutionary success may be due to the extended dikaryotic stage of their life cycle, which is the basis for their scientific name: the Dikarya. Dikaryosis is maintained by similar structures, the clamp in basidiomycetes and the crozier in ascomycetes. Homeodomain transcription factors are required for clamp formation in all basidiomycetes studied. We identified all the homeobox genes in the filamentous ascomycete fungus Podospora anserina and constructed deletion mutants for each of these genes and for a number of gene combinations. Croziers developed normally in these mutants, including those with up to six deleted homeogenes. However, some mutants had defects in maturation of the fruiting body, an effect that could be rescued by providing wild-type maternal hyphae. Analysis of mutants deficient in multiple homeogenes revealed interactions between the genes, suggesting that they operate as a complex network. Similar to their role in animals and plants, homeodomain transcription factors in ascomycetes are involved in shaping multicellular structures.
Highlights
Often inconspicuous, Eumycota fungi constitute one of the dominant life forms of our planet
Identification of homeobox genes in P. anserina A search of the P. anserina genome using the sequence of pah1 and HD transcription factors from N. crassa and M. grisea [16,17] as queries revealed the presence of seven genes coding for putative
PAH7 was not identified by Kim et al because the corresponding gene is located in a region that contained numerous sequencing errors. After correction of these errors, we were able to identify pah7 as a seventh homeobox gene, which was orthologous to MoHOX4 ( = MGG_06285), the only M. grisea transcription factor without a P. anserina ortholog in the study by Kim et al [17]
Summary
Eumycota fungi constitute one of the dominant life forms of our planet They inhabit most biotopes and their total biomass is huge [1]. During evolution, they have diversified to an estimated one million or more species [2] and have adopted many lifestyles including saprotrophy, mutualistic interactions with plants, algae and animals, and parasitic association with most eukaryote groups. The two haploid nuclei fuse in cells known as basidia and asci in the basidiomycetes and ascomycetes, respectively. The resulting structures are known as clamp connection in basidiomycetes and crozier in ascomycetes
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