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The Plant Infection Test: Spray and Wound-Mediated Inoculation with the Plant Pathogen Magnaporthe Grisea
Published on: August 4, 2018
Karyotypic Variation within Clonal Lineages of the Rice Blast Fungus, Magnaporthe grisea
1Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907.
Abstract:
We have analyzed the karyotype of the rice blast fungus, Magnaporthe grisea, by using pulsed-filed gel electrophoresis. We tested whether the electrophoretic karyotype of an isolate was related to its pathotype, as determined by infection assays, or its genetic lineage, as determined by DNA fingerprinting. Highly reproducible electrophoretic karyotypes were obtained for a collection of U.S. and Chinese isolates representing a diverse collection of pathotypes and genetic lineages. Chromosomes ranged in size from 3 to 10 Mb. Although chromosome number was largely invariant, chromosome length polymorphisms were frequent. Minichromosomes were also found, although their presence was not ubiquitous. They ranged in number from 1 to 3 and in size from 470 kb to 2.2 Mb. Karyotypes were sufficiently variable as to obscure the obvious relatedness of isolates on the basis of pathogenicity assays or genetic lineage analysis by DNA fingerprinting. We documented that the electrophoretic karyotype of an isolate can change after prolonged serial transfer in culture and that this change did not alter the isolate's pathotype. The mechanisms bringing about karyotype variability involve deletions, translocations, and more complex rearrangements. We conclude that karyotypic variability in the rice blast fungus is a reflection of the lack of sexuality in wild populations which leads to the maintenance of neutral genomic rearrangements in clones of the fungus.
Insights
The karyotype of the rice blast fungus, Magnaporthe grisea, shows significant variability due to genomic rearrangements. This variability, however, does not affect the fungus
Area of Science:
- Mycology
- Genetics
- Plant Pathology
Background:
- Magnaporthe grisea is a significant pathogen causing rice blast disease globally.
- Understanding the genetic makeup and variability of M. grisea is crucial for disease management.
- Previous studies have utilized DNA fingerprinting, but karyotype analysis offers a broader genomic perspective.
Purpose of the Study:
- To analyze the electrophoretic karyotype of Magnaporthe grisea isolates.
- To investigate the relationship between karyotype, pathotype, and genetic lineage.
- To understand the mechanisms and implications of karyotypic variability in M. grisea.
Main Methods:
- Pulsed-field gel electrophoresis (PFGE) was employed to analyze the karyotypes of diverse M. grisea isolates.
- Infection assays were used to determine pathotypes.
- DNA fingerprinting was performed to assess genetic lineage.
Main Results:
- Reproducible electrophoretic karyotypes were obtained, revealing chromosome sizes ranging from 3 to 10 Mb.
- Frequent chromosome length polymorphisms and the presence of minichromosomes (470 kb to 2.2 Mb) were observed.
- Karyotypic variability was substantial, often obscuring relationships based on pathogenicity or genetic lineage; karyotype changes occurred during prolonged culture without altering pathotype.
Conclusions:
- Karyotypic variability in M. grisea is extensive and driven by mechanisms including deletions, translocations, and complex rearrangements.
- The observed variability is likely a consequence of the lack of sexual reproduction in wild populations, promoting the maintenance of neutral genomic changes in clonal lineages.
- Karyotypic instability does not necessarily correlate with changes in pathogenicity, highlighting the complexity of fungal genome evolution.
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