title: Genetic Analyses of the Internal Transcribed Spacer Sequences Suggest Introgression and Duplication in the Medicinal Mushroom Agaricus subrufescens.
abstract: The internal transcribed spacer (ITS) region of the nuclear ribosomal RNA gene cluster is widely used in fungal taxonomy and phylogeographic studies. The medicinal and edible mushroom Agaricus subrufescens has a worldwide distribution with a high level of polymorphism in the ITS region. A previous analysis suggested notable ITS sequence heterogeneity within the wild French isolate CA487. The objective of this study was to investigate the pattern and potential mechanism of ITS sequence heterogeneity within this strain. Using PCR, cloning, and sequencing, we identified three types of ITS sequences, A, B, and C with a balanced distribution, which differed from each other at 13 polymorphic positions. The phylogenetic comparisons with samples from different continents revealed that the type C sequence was similar to those found in Oceanian and Asian specimens of A. subrufescens while types A and B sequences were close to those found in the Americas or in Europe. We further investigated the inheritance of these three ITS sequence types by analyzing their distribution among single-spore isolates from CA487. In this analysis, three co-dominant markers were used firstly to distinguish the homokaryotic offspring from the heterokaryotic offspring. The homokaryotic offspring were then analyzed for their ITS types. Our genetic analyses revealed that types A and B were two alleles segregating at one locus ITSI, while type C was not allelic with types A and B but was located at another unlinked locus ITSII. Furthermore, type C was present in only one of the two constitutive haploid nuclei (n) of the heterokaryotic (n+n) parent CA487. These data suggest that there was a relatively recent introduction of the type C sequence and a duplication of the ITS locus in this strain. Whether other genes were also transferred and duplicated and their impacts on genome structure and stability remain to be investigated.
authors.affiliation: INRA, MycSA, Villenave d'Ornon, France.|Center of Excellence in Fungal Research, Mae Fah Luang University, Chiang Rai, Thailand.|School of Science, Mae Fah Luang University, Chiang Rai, Thailand.
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.affiliation: INRA, MycSA, Villenave d'Ornon, France.
authors.forename: Magalie
authors.initials: M
authors.lastname: Moinard
authors.affiliation: Department of Biology, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Jianping
authors.initials: J
authors.lastname: Xu
authors.affiliation: Institute of Plant and Environment Protection, Beijing Academy of Agriculture and Forestry Sciences, Beijing, China.|Beijing Engineering Research Center for Edible Mushroom, Beijing, China.
authors.forename: Shouxian
authors.initials: S
authors.lastname: Wang
authors.affiliation: INRA, MycSA, Villenave d'Ornon, France.
authors.forename: Marie
authors.initials: M
authors.lastname: Foulongne-Oriol
authors.affiliation: State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Ruilin
authors.initials: R
authors.lastname: Zhao
authors.affiliation: Center of Excellence in Fungal Research, Mae Fah Luang University, Chiang Rai, Thailand.|School of Science, Mae Fah Luang University, Chiang Rai, Thailand.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Hyde
authors.affiliation: INRA, MycSA, Villenave d'Ornon, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Callac
mesh_terms: D000364:Agaricus / Q000145:classification* / Q000235:genetics* / Q000254:growth & development; D001483:Base Sequence; D004271:DNA, Fungal / Q000235:genetics*; D021903:DNA, Ribosomal Spacer / Q000235:genetics*; D005784:Gene Amplification; D005820:Genetic Testing / Q000379:methods*; D005838:Genotype; D006579:Heterozygote; D010802:Phylogeny; D017422:Sequence Analysis, DNA / Q000379:methods*; D012689:Sequence Homology, Nucleic Acid
chemical_list: D004271:DNA, Fungal; D021903:DNA, Ribosomal Spacer