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Genomic rearrangements generate hypervariable mini-chromosomes in host-specific isolates of the blast fungus.

ABSTRACT: Supernumerary mini-chromosomes-a unique type of genomic structural variation-have been implicated in the emergence of virulence traits in plant pathogenic fungi. However, the mechanisms that facilitate the emergence and maintenance of mini-chromosomes across fungi remain poorly understood. In the blast fungus Magnaporthe oryzae (Syn. Pyricularia oryzae), mini-chromosomes have been first described in the early 1990s but, until very recently, have been overlooked in genomic studies. Here we investigated structural variation in four isolates of the blast fungus M. oryzae from different grass hosts and analyzed the sequences of mini-chromosomes in the rice, foxtail millet and goosegrass isolates. The mini-chromosomes of these isolates turned out to be highly diverse with distinct sequence composition. They are enriched in repetitive elements and have lower gene density than core-chromosomes. We identified several virulence-related genes in the mini-chromosome of the rice isolate, including the virulence-related polyketide synthase Ace1 and two variants of the effector gene AVR-Pik. Macrosynteny analyses around these loci revealed structural rearrangements, including inter-chromosomal translocations between core- and mini-chromosomes. Our findings provide evidence that mini-chromosomes emerge from structural rearrangements and segmental duplication of core-chromosomes and might contribute to adaptive evolution of the blast fungus.

SUBMITTER: Langner T

PROVIDER: S-EPMC7909708 | biostudies-literature | 2021 Feb

REPOSITORIES: biostudies-literature

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Genomic rearrangements generate hypervariable mini-chromosomes in host-specific isolates of the blast fungus.

Langner Thorsten T Harant Adeline A Gomez-Luciano Luis B LB Shrestha Ram K RK Malmgren Angus A Latorre Sergio M SM Burbano Hernán A HA Win Joe J Kamoun Sophien S

PLoS genetics 20210216 2

Supernumerary mini-chromosomes-a unique type of genomic structural variation-have been implicated in the emergence of virulence traits in plant pathogenic fungi. However, the mechanisms that facilitate the emergence and maintenance of mini-chromosomes across fungi remain poorly understood. In the blast fungus Magnaporthe oryzae (Syn. Pyricularia oryzae), mini-chromosomes have been first described in the early 1990s but, until very recently, have been overlooked in genomic studies. Here we invest ...[more]

PMID: 33591993

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Project description:Precise kinetochore-microtubule interactions ensure faithful chromosome segregation in eukaryotes. Centromeres, identified as scaffolding sites for kinetochore assembly, are among the most rapidly evolving chromosomal loci in terms of the DNA sequence and length and organization of intrinsic elements. Neither the centromere structure nor the kinetochore dynamics is well studied in plant-pathogenic fungi. Here, we sought to understand the process of chromosome segregation in the rice blast fungus Magnaporthe oryzae High-resolution imaging of green fluorescent protein (GFP)-tagged inner kinetochore proteins CenpA and CenpC revealed unusual albeit transient declustering of centromeres just before anaphase separation of chromosomes in M. oryzae Strikingly, the declustered centromeres positioned randomly at the spindle midzone without an apparent metaphase plate per se Using CenpA chromatin immunoprecipitation followed by deep sequencing, all seven centromeres in M. oryzae were found to be regional, spanning 57-kb to 109-kb transcriptionally poor regions. Highly AT-rich and heavily methylated DNA sequences were the only common defining features of all the centromeres in rice blast. Lack of centromere-specific DNA sequence motifs or repetitive elements suggests an epigenetic specification of centromere function in M. oryzae PacBio genome assemblies and synteny analyses facilitated comparison of the centromeric/pericentromeric regions in distinct isolates of rice blast and wheat blast and in Magnaporthiopsis poae Overall, this study revealed unusual centromere dynamics and precisely identified the centromere loci in the top model fungal pathogens that belong to Magnaporthales and cause severe losses in the global production of food crops and turf grasses.IMPORTANCEMagnaporthe oryzae is an important fungal pathogen that causes a loss of 10% to 30% of the annual rice crop due to the devastating blast disease. In most organisms, kinetochores are clustered together or arranged at the metaphase plate to facilitate synchronized anaphase separation of sister chromatids in mitosis. In this study, we showed that the initially clustered kinetochores separate and position randomly prior to anaphase in M. oryzae Centromeres in M. oryzae occupy large genomic regions and form on AT-rich DNA without any common sequence motifs. Overall, this study identified atypical kinetochore dynamics and mapped functional centromeres in M. oryzae to define the roles of centromeric and pericentric boundaries in kinetochore assembly on epigenetically specified centromere loci. This study should pave the way for further understanding of the contribution of heterochromatin in genome stability and virulence of the blast fungus and its related species of high economic importance.

Project description:Transcriptional changes were monitored in the wheat cultivar Renan 24 hours post i noculation with adapted and non-adapted Magnaporthe isolates using the Affymetrix wheat genome array GeneChip®. Wheat plants cv. Renan were grown in a peat and sand (1:1) mix at 23 C in a Sanyo Fitotron growth cabinet (Sanyo Gallenkamp PLC, Loughborough, U.K.) with a 16/8 h, light/dark cycle. Three Magnaporthe isolates were used in this expt, two wheat-adapted isolates (BR32, BR37) and one wheat non-adapted isolate (BR29). Magnaporthe isolates were grown for eleven days on Complete Media Agar at 25 C under a 16/8h, light/dark cycle. Conidia were harvested by flooding the plates with 5 mL of sterile inoculation solution [0.25% (w/v) gelatine and 0.01% (v/v) Tween 20] and scraping the conidia from the surface using a sterile glass rod. Conidia were filtered through sterile miracloth and the density adjusted to 1 x 10 5 conidia mL-1 with inoculation solution. Fourteen day old wheat seedlings mist inoculated with 4 mL of a Magnaporthe conidia suspension and plants were sealed in plastic propagators to maintain relative humidity c.100% and kept at 25 C in the dark for the first 24 hours post inoculation (hpi). Inoculation solution without Magnaporthe conidia was used as a mock-inoculation control. Leaf samples were collected 24 hpi for transcriptomics analysis from three independent biological experiments. Leaf tissue was ground under liquid nitrogen and total RNA extracted using a QIAquick RNeasy Plant Extraction Kit (Qiagen, Hilden, Germany), followed by TURBO DNaseTM (Ambion, Texas, U.S.A.) treatment. RNeasy Mini Spin column purification (Qiagen) was used to further purify RNA samples for array hybridisation. RNA quality checks, cRNA conversion and Affymetrix genome array hybridisation was carried out by the Nottingham Arabidopsis Stock Centre (NASC) array hybridisation service (http://affymetrix.arabidopsis.info/). ****[PLEXdb(http://www.plexdb.org) has submitted this series at GEO on behalf of the original contributor, Graham McGrann. The equivalent experiment is TA24 at PLEXdb.]

Dataset Information

Genomic rearrangements generate hypervariable mini-chromosomes in host-specific isolates of the blast fungus.

Publications

Genomic rearrangements generate hypervariable mini-chromosomes in host-specific isolates of the blast fungus.

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