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Home • Ascobolus immersus RN42 v1.0
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Ascobolus immersus asci. Wild-type brown spores as opposed to mutant white and dotted ascospores. © Fabienne Malagnac

Ascobolus immersus Pers. Fr. is a cosmopilitan heterothallic ascomycota (Pezizales) living on herbivore dung (coprophilous). Its sexual reproduction results in asci containing 8 uninucleate ascospores that are actively discharged to land away from the fruiting bodies also called apothecia. As opposed to the vast majority of the ascomycota, such as Neurospora crassa or Aspergillus nidulans, A. immersus does not form asexual conidia. Sexual reproduction is therefore its only way to propagate. In the late 1930s, Prof. G. Rizet introduced A. immersus in his laboratory as a model organism for genetic studies. On appropriate axenic media, A. immersus completes its sexual cycle within two weeks and its ascospores germinate efficiently. It can be transformed, allowing reverse genetic approaches and expression of heterologous genes. Originally used to study meiotic recombination, A. immersus also contributed to a better understanding of epigenetic phenomena in fungi. Indeed, this fungus is endowed with a homology-based transcriptional gene silencing system named Methylation Induced Premeiotically (MIP) system. During sexual reproduction, MIP heavily methylates the cytosine residues of any artificial or natural DNA repeats, providing they share at least 400 base-pair of identity. As a result, the transcription of genes carried by MIPed sequences is inhibited. A. immersus belongs to the class of Pezizomycetes for which few complete genome sequences are available. To date, its closest relative that has been already sequenced is the ectomycorrhizal black truffle, Tuber melanosporum. Sequencing the A. immersus genome will thus allow fruitful comparative genomic approaches between these two species that display radically different lifestyles and reproductive strategies. Moreover, because A. immersus is a model organism easily tractable in laboratory conditions, it might contribute to develop molecular tools which would be out of reach in T. melanosporum. A. immersus sequencing is carried out within the framework of the 1000 Fungal Genome Project (F1000). The overarching goal of F1000 is to inform all areas of fungal biology by providing broad, genomic coverage of Kingdom Fungi (Fungi). The sampling design is based on a phylogenetic framework developed by the Assembly the Fungal Tree of Life Project and is focused on covering all major subordinal groups (clades) of Fungi.

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