A detailed analysis of the recombination landscape of the button mushroom Agaricus bisporus var. bisporus

Abstract

The button mushroom (Agaricus bisporus) is one of the world's most cultivated mushroom species, but in spite of its economic importance generation of new cultivars by outbreeding is exceptional. Previous genetic analyses of the white bisporus variety, including all cultivars and most wild isolates revealed that crossing over frequencies are low, which might explain the lack of introducing novel traits into existing cultivars. By generating two high quality whole genome sequence assemblies (one de novo and the other by improving the existing reference genome) of the first commercial white hybrid Horst U1, a detailed study of the crossover (CO) landscape was initiated. Using a set of 626 SNPs in a haploid offspring of 139 single spore isolates and whole genome sequencing on a limited number of homo- and heterokaryotic single spore isolates, we precisely mapped all COs showing that they are almost exclusively restricted to regions of about 100kb at the chromosome ends. Most basidia of A. bisporus var. bisporus produce two spores and pair preferentially via non-sister nuclei. Combined with the COs restricted to the chromosome ends, these spores retain most of the heterozygosity of the parent thus explaining how present-day white cultivars are genetically so close to the first hybrid marketed in 1980. To our knowledge this is the first example of an organism which displays such specific CO landscape.

Multi-trait QTL analysis for agronomic and quality characters of Agaricus bisporus (button mushrooms)

“…1). Horst U1 represents the present standard for agronomic and quality traits for button mushroom since most present-day commercial white varieties are derived from this hybrid (Sonnenberg et al 2016). In this way we can see how the introduction of wild germplasm affects its important traits.…”

“…SNP markers used for genotyping were selected to make them evenly distribute based on the genome sequences of the homokaryon H97 (Morin et al 2012). Nevertheless, the linkage maps are very short with regions of low resolution because of the low recombination frequency observed mainly due to restriction of CO at chromosome ends (Sonnenberg et al 2016). The QTL mapping is thus restricted in most cases to assigning QTLs to chromosomes.…”

“…The first hybrid cultivar Horst U1 (Fritsche 1981), was released in the 1980s. Subsequent new varieties were identical or very similar to this first hybrid indicating that these were all varieties derived from the first hybrid line (Sonnenberg et al 2005, 2016). Mushroom breeding has been so far an applied science and new varieties have been generated mainly modifying existing varieties by selecting fertile single spore cultures or by generating multi spore cultures.…”

“…Offspring of A. bisporus var. bisporus show crossover (CO) mainly restricted to regions ca 100 kb from chromosome ends (Sonnenberg et al 2016). Offspring of hybrids between the A. bisporus var.…”

Evaluation of king oyster mushroom strains (Pleurotus eryngii) on selective lignin degradation in wheat straw: An update

“…(Sonnenberg et al 2016). The DNA samples of the P. eryngii were subsequently used a low complexity sequencing method.…”