![]() The genetic base for both phenotypes, however, are unknown. The trait basidial spore number (BSN) has been mapped previously on chromosome 1 9. ![]() The availability of complete and well annotated genomes of both subspecies can help to unravel the genetic components underlying the differences in basidial spore number and recombination landscape. The cumbersome isolation of homokaryotic offspring (only few % of spores are haploid) and especially the restriction of recombination to chromosome ends hampers an efficient breeding of var. burnettii indicated that burnettii shows a more even distribution of crossovers over the chromosomes 9. In contrast, linkage maps generated with offspring of var. bisporus, crossovers are mainly restricted to chromosome ends 8. Previous research has also shown that the two subspecies differ in distribution of meiotic recombination over the chromosomes. burnettii is mainly heterothallic and has four-spored basidia 5, 6, 7. While the former subspecies has a mainly secondary homothallic life cycle where basidia produce two spores, var. bisporus will therefore remain the dominant commercial variety, and thus the platform for breeding for the time being. Especially the production of abundant numbers of small mushrooms that show a quick maturation (cap opening) and asymmetric caps are considered as poor quality. Despite a few beneficial traits such as resistance to some diseases 2, 3, the average quality of var. All commercial varieties and most wild isolates are represented by the subspecies var. ![]() It is an amphithallic basidiomycete represented mainly by two subspecies, i.e., Agaricus bisporus var. A good example of a species with different life cycles is the button mushroom Agaricus bisporus, one of the most cultivated edible mushrooms in the world. Especially complete and well annotated genomes of subspecies, with different life cycles, are a prerequisite to study the relation between genomic content and effects on different life cycles. However, most genome sequences typify only one strain of a species, do not represent telomere-to-telomere chromosomes, do not have an accurate annotation of transposable elements, and centromeres remain unidentified. Recently, the genome sequence of 90 mushrooms has been published 1, but especially the ongoing 1,000 Fungal Genomes Project ( ) will generate an extensive insight into the genomes of a wide range of fungal families and species. The last decade has shown a sharp increase in the number of sequenced fungal genomes. The new findings using the exceptionally complete and well annotated genomes of this basidiomycete demonstrate the importance for unravelling genetic components underlying the different life cycles. burnettii confirmed an even distribution of crossovers in meiosis, contrasting the recombination landscape of var. ![]() ![]() A single large cluster of repeats was found on each chromosome at the same respective position in all strains, harbouring nearly 50% of all repeats and likely representing centromeres. The genomes of both subspecies were largely co-linear, and especially the chromosome ends differed in gene model content between the two subspecies. The genomes were assembled into telomere-to-telomere chromosomes and a consistent set of gene predictions was generated. To better understand the relationship between genomic make-up and different lifestyles, we have de novo sequenced a burnettii homokaryon and synchronised gene annotations with updated versions of the published genomes of var. burnettii is heterothallic with recombination seemingly equally distributed over the chromosomes. bisporus has a secondarily homothallic life cycle with recombination restricted to chromosome ends, while var. Agaricus bisporus, the most cultivated edible mushroom worldwide, is represented mainly by the subspecies var. ![]()
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