Mini-Chromosomes as Horizontal Gene Shuttles in the Multihost Blast Fungus

• Applicant: Dr. Cristina Barragan
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems ; General Genetics and Functional Genome Biology ; Plant Breeding and Plant Pathology ; Metabolism, Biochemistry and Genetics of Microorganisms
• Term: from 2022 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 506550091

• Final Report Year: 2024

Final Report Abstract

The blast fungus, Magnaporthe oryzae, is a highly devastating plant pathogen that infects both wild grasses and staple cereal crops such as rice and wheat. In recent years, the spread of blast disease, caused by this fungus, has escalated, likely due to the international trade of infected seeds and climate change, making it a major threat to global cereal agriculture. During my Walter Benjamin-funded project, two main findings emerged. Firstly, we discovered that the blast fungus is present in southern Germany and infects wild grasses. This region was previously considered too cold for its survival, indicating a potential northward migration of the fungus, potentially facilitated by global warming. Furthermore, laboratory experiments revealed that these isolates infecting wild grasses in Germany can also infect wheat and barley under controlled conditions. Since host jumps between isolates infecting wild hosts and cultivated grasses have previously led to blast disease pandemics, these findings highlight a latent risk to European cereal production. The second major finding was that the blast fungus can horizontally exchange genetic material through the transfer of accessory mini-chromosomes. I demonstrated that mini-chromosome transfer can occur under natural field conditions between isolates infecting wild grasses and those infecting crops. Preliminary observations of my work also show that horizontal mini-chromosome acquisition has an impact on major biological processes such as reproductive strategy, disease and host range. By acquiring new genetic material through mini-chromosomes, clonal isolates infecting crops, which are characterized by reduced genetic diversity, can more readily adapt to their hosts, ultimately contributing to the spread of blast disease. The findings of this project have direct implications for agricultural practices. On one hand, they underscore the importance of monitoring blast disease not only on cereal crops but also on wild grasses. On the other hand, detecting horizontal gene flow between isolates can inform blast disease management strategies, such as selective weeding or strategic fungicide use to limit gene exchange and curb pathogen evolution.

Publications

• Genome assemblies of the blast fungus Magnaporthe (Syn. Pyricularia) spp. collected from wild grasses in Germany (2022)
  Barragan, A.C., Win, J., Harant, A., Kamoun, S. & Langner, T.
  
• Wild grass isolates of Magnaporthe (Syn. Pyricularia ) spp. from Germany can cause blast disease on cereal crops.
  Barragan, A. Cristina; Latorre, Sergio M.; Mock, Paul G.; Harant, Adeline; Win, Joe; Malmgren, Angus; Burbano, Hernán A.; Kamoun, Sophien & Langner, Thorsten
  
• Increased genetic diversity of clonal rice blast fungus lineages through multiple mini-chromosome transfers (2024) Zenodo, Poster presented at 32nd Fungal Genetics Conference, Pacific Grove, CA, USA
  Barragan, A.C., Latorre, S.M., Malmgren, A., Harant, A., Win, J., Sugihara, Y., Burbano, H.A., Kamoun, S. & Langner, T.
  
• Multiple Horizontal Mini-chromosome Transfers Drive Genome Evolution of Clonal Blast Fungus Lineages. Molecular Biology and Evolution, 41(8).
  Barragan, Ana Cristina; Latorre, Sergio M.; Malmgren, Angus; Harant, Adeline; Win, Joe; Sugihara, Yu; Burbano, Hernán A.; Kamoun, Sophien & Langner, Thorsten