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Aanen DK, van ’t Padje A, Auxier B. Longevity of Fungal Mycelia and Nuclear Quality Checks: a New Hypothesis for the Role of Clamp Connections in Dikaryons. Microbiol Mol Biol Rev 2023; 87:e0002221. [PMID: 37409939 PMCID: PMC10521366 DOI: 10.1128/mmbr.00022-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/07/2023] Open
Abstract
This paper addresses the stability of mycelial growth in fungi and differences between ascomycetes and basidiomycetes. Starting with general evolutionary theories of multicellularity and the role of sex, we then discuss individuality in fungi. Recent research has demonstrated the deleterious consequences of nucleus-level selection in fungal mycelia, favoring cheaters with a nucleus-level benefit during spore formation but a negative effect on mycelium-level fitness. Cheaters appear to generally be loss-of-fusion (LOF) mutants, with a higher propensity to form aerial hyphae developing into asexual spores. Since LOF mutants rely on heterokaryosis with wild-type nuclei, we argue that regular single-spore bottlenecks can efficiently select against such cheater mutants. We then zoom in on ecological differences between ascomycetes being typically fast-growing but short-lived with frequent asexual-spore bottlenecks and basidiomycetes being generally slow-growing but long-lived and usually without asexual-spore bottlenecks. We argue that these life history differences have coevolved with stricter nuclear quality checks in basidiomycetes. Specifically, we propose a new function for clamp connections, structures formed during the sexual stage in ascomycetes and basidiomycetes but during somatic growth only in basidiomycete dikaryons. During dikaryon cell division, the two haploid nuclei temporarily enter a monokaryotic phase, by alternatingly entering a retrograde-growing clamp cell, which subsequently fuses with the subapical cell to recover the dikaryotic cell. We hypothesize that clamp connections act as screening devices for nuclear quality, with both nuclei continuously testing each other for fusion ability, a test that LOF mutants will fail. By linking differences in longevity of the mycelial phase to ecology and stringency of nuclear quality checks, we propose that mycelia have a constant and low lifetime cheating risk, irrespective of their size and longevity.
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Affiliation(s)
- Duur K. Aanen
- Department of Plant Sciences, Laboratory of Genetics, Wageningen University, Wageningen, The Netherlands
| | - Anouk van ’t Padje
- Department of Plant Sciences, Laboratory of Genetics, Wageningen University, Wageningen, The Netherlands
| | - Benjamin Auxier
- Department of Plant Sciences, Laboratory of Genetics, Wageningen University, Wageningen, The Netherlands
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Lassagne A, Brun S, Malagnac F, Adreit H, Milazzo J, Fournier E, Tharreau D. Male fertility in Pyricularia oryzae: Microconidia are spermatia. Environ Microbiol 2022; 24:6365-6375. [PMID: 36165613 PMCID: PMC10092719 DOI: 10.1111/1462-2920.16226] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Accepted: 09/25/2022] [Indexed: 01/12/2023]
Abstract
Sexual reproduction in Ascomycetes is well described in several model organisms such as Neurospora crassa or Podospora anserina. Deciphering the biological process of sexual reproduction (from the recognition between compatible partners to the formation of zygote) can be a major advantage to better control sexually reproducing pathogenic fungi. In Pyricularia oryzae, the fungal pathogen causing blast diseases on several Poaceae species, the biology of sexual reproduction remains poorly documented. Besides the well-documented production of asexual macroconidia, the production of microconidia was seldom reported in P. oryzae, and their role as male gamete (i.e., spermatia) and in male fertility has never been explored. Here, we characterised the morphological features of microconidia and demonstrated that they are bona fide spermatia. Contrary to macroconidia, microconidia are not able to germinate and seem to be the only male gametes in P. oryzae. We show that fruiting body (perithecium) formation requires microconidia to get in contact with mycelium of strains of opposite mating type, to presumably fertilise the female gametes.
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Affiliation(s)
- Alexandre Lassagne
- Plant Health Institute of Montpellier (PHIM), CIRAD, Montpellier, France.,Plant Health Institute of Montpellier (PHIM), University of Montpellier, CIRAD, INRAE, Institut Agro, IRD, Montpellier, France
| | - Sylvain Brun
- Institut Jacques Monod, Université Paris Cité, CNRS, Paris, France
| | - Fabienne Malagnac
- Institute for Integrative Biology of the Cell (I2BC), Université Paris-Saclay, CEA, CNRS, Gif-sur-Yvette, France
| | - Henri Adreit
- Plant Health Institute of Montpellier (PHIM), CIRAD, Montpellier, France
| | - Joëlle Milazzo
- Plant Health Institute of Montpellier (PHIM), CIRAD, Montpellier, France
| | - Elisabeth Fournier
- Plant Health Institute of Montpellier (PHIM), University of Montpellier, CIRAD, INRAE, Institut Agro, IRD, Montpellier, France
| | - Didier Tharreau
- Plant Health Institute of Montpellier (PHIM), CIRAD, Montpellier, France
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Orellana-Torrejon C, Vidal T, Gazeau G, Boixel AL, Gélisse S, Lageyre J, Saint-Jean S, Suffert F. Multiple scenarios for sexual crosses in the fungal pathogen Zymoseptoria tritici on wheat residues: Potential consequences for virulence gene transmission. Fungal Genet Biol 2022; 163:103744. [PMID: 36209959 DOI: 10.1016/j.fgb.2022.103744] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Revised: 08/31/2022] [Accepted: 09/30/2022] [Indexed: 01/06/2023]
Abstract
Little is known about the impact of host immunity on sexual reproduction in fungal pathogens. In particular, it is unclear whether crossing requires both sexual partners to infect living plant tissues. We addressed this issue in a three-year experiment investigating different scenarios of Zymoseptoria tritici crosses according to the virulence ('vir') or avirulence ('avr') of the parents against a qualitative resistance gene. Co-inoculations ('vir × vir', 'avr × vir', 'avr × avr') and single inoculations were performed on a wheat cultivar carrying the Stb16q resistance gene (Cellule) and a susceptible cultivar (Apache), in the greenhouse. We assessed the intensity of asexual reproduction by scoring disease severity, and the intensity of sexual reproduction by counting the ascospores discharged from wheat residues. As expected, disease severity was more intense on Cellule for 'vir × vir' co-inoculations than for 'avr × vir' co-inoculations, with no disease for 'avr × avr'. However, all types of co-inoculation yielded sexual offspring, whether or not the parental strains caused plant symptoms. Parenthood was confirmed by genotyping (SSR markers), and the occurrence of crosses between (co-)inoculated and exogenous strains (other strains from the experiment, or from far away) was determined. We showed that symptomatic asexual infection was not required for a strain to participate in sexual reproduction, and deduced from this result that avirulent strains could be maintained asymptomatically "on" or "in" leaf tissues of plants carrying the corresponding resistant gene for long enough to reproduce sexually. In two of the three years, the intensity of sexual reproduction did not differ between the three types of co-inoculation in Cellule, suggesting that crosses involving avirulent strains are not anecdotal. We discuss the possible mechanisms explaining the maintenance of avirulence in Z. tritici populations and the potential impact of particular resistance deployments such as cultivar mixtures for limiting resistance breakdown.
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Affiliation(s)
- Carolina Orellana-Torrejon
- Université Paris-Saclay, INRAE, UR BIOGER, 91120 Palaiseau, France; Université Paris-Saclay, INRAE, AgroParisTech, UMR ECOSYS, 91120 Palaiseau, France
| | - Tiphaine Vidal
- Université Paris-Saclay, INRAE, UR BIOGER, 91120 Palaiseau, France
| | - Gwilherm Gazeau
- Université Paris-Saclay, INRAE, UR BIOGER, 91120 Palaiseau, France
| | - Anne-Lise Boixel
- Université Paris-Saclay, INRAE, UR BIOGER, 91120 Palaiseau, France
| | - Sandrine Gélisse
- Université Paris-Saclay, INRAE, UR BIOGER, 91120 Palaiseau, France
| | - Jérôme Lageyre
- Université Paris-Saclay, INRAE, AgroParisTech, UMR ECOSYS, 91120 Palaiseau, France
| | - Sébastien Saint-Jean
- Université Paris-Saclay, INRAE, AgroParisTech, UMR ECOSYS, 91120 Palaiseau, France
| | - Frédéric Suffert
- Université Paris-Saclay, INRAE, UR BIOGER, 91120 Palaiseau, France.
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