A DNA Damage Checkpoint Pathway Coordinates the Division of Dikaryotic Cells in the Ink Cap MushroomCoprinopsis cinerea

Abstract

The fungal fruiting body or mushroom is a multicellular structure essential for sexual reproduction. It is composed of dikaryotic cells that contain one haploid nucleus from each mating partner sharing the same cytoplasm without undergoing nuclear fusion. In the mushroom, the pileus bears the hymenium, a layer of cells that includes the specialized basidia in which nuclear fusion, meiosis, and sporulation occur. Coprinopsis cinerea is a well-known model fungus used to study developmental processes associated with the formation of the fruiting body. Here we describe that knocking down the expression of Atr1 and Chk1, two kinases shown to be involved in the response to DNA damage in a number of eukaryotic organisms, dramatically impairs the ability to develop fruiting bodies in C. cinerea, as well as other developmental decisions such as sclerotia formation. These developmental defects correlated with the impairment in silenced strains to sustain an appropriated dikaryotic cell cycle. Dikaryotic cells in which chk1 or atr1 genes were silenced displayed a higher level of asynchronous mitosis and as a consequence aberrant cells carrying an unbalanced dose of nuclei. Since fruiting body initiation is dependent on the balanced mating-type regulator doses present in the dikaryon, we believe that the observed developmental defects were a consequence of the impaired cell cycle in the dikaryon. Our results suggest a connection between the DNA damage response cascade, cell cycle regulation, and developmental processes in this fungus. IN fungal cells, mating-the process equivalent to fertilizationbrings together two haploid nuclei in the same cytoplasm. It is generally thought that this process is essentially followed by nuclear fusion, resulting in a diploid nucleus that either enters meiosis immediately (as occurs in the fission yeast Schizosaccharomyces pombe) or is maintained and proliferates in the diploid state (as happens in the budding yeast Saccharomyces cerevisiae). However, in a large number of fungi, mating does not result in diploid nuclei. Instead, they form dikaryons, cells that contain one haploid nucleus from each mating partner sharing the same cytoplasm for a period of time without undergoing nuclear fusion or meiosis. These dikaryons continue to propagate, and eventually nuclear fusion will take place, which will be followed by meiosis, closing the sexual cycle (Brown and Casselton 2001).Dikaryon cell division, also called conjugate division, represents a big challenge to the cell since it has to ensure that each daughter dikaryon inherits a balance of each parental genome. For that, a complex cell cycle is required that involves distinct mechanisms to maintain heterokaryosis after cell division. For example, for a large number of Basidiomycota (e.g., the mushroom Coprinopsis cinerea), conjugate division includes the formation of a structure known as the clamp connection or clamp cell, as well as the sorting of one of the nuclei to this structure (Casselton 1978;Brown and Casselton 2001). In the...

Comparative genomics reveals unique wood‐decay strategies and fruiting body development in the Schizophyllaceae

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Cytoplasmic retention and degradation of a mitotic inducer enable plant infection by a pathogenic fungus

“…In any case, the final result will be a cell cycle arrested filament (by virtue of b-factor) and therefore it will be proficient for infection, explaining the ability of mutant cells to infect corn plants. Interestingly, this ability to synchronize the cell cycle status of distinct nuclei in a common cytoplasm by homeodomain proteins of the b-factor family is the basis for accurate cell division in other basidiomycete dikaryotic fungi such as Coprinopsis cinerea (de Sena-Tomás et al, 2013).…”

Virulence-specific cell cycle and morphogenesis connections in pathogenic fungi

“…This uncoupling between mitosis and penetration in U. maydis is probably a consequence of the peculiarities of the complex cell cycle required to maintain heterokaryosis after cell division. In some basidiomycetes, as is the case for U. maydis and Coprinopsis cinerea, nuclear division involves the production of a specific structure called the clamp-like cell [72][73][74], devoted microtubule structures [75], and the activation of a specific checkpoint controlled by the DDR pathway [52,72]. Again, it makes sense that during the penetration step, which in U. maydis is apparently not dependent on turgor pressure but on continuous communication between the plant and the fungus that involves the dedicated secretion of effector proteins, mitosis has to be delayed.…”