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

• Applicant: Cristina Barragan, Ph.D.
• 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

Magnaporthe oryzae is a highly devastating plant pathogen that infects a variety of cereal crops and wild grasses. To date, most M. oryzae strains responsible for crop pandemics are of clonal origin and reproduce asexually. Despite their lack of genetic shuffling via recombination, clonal M. oryzae are able to quickly adapt to their host and overcome disease resistance, posing a major challenge in developing blast resistant crops. This raises the question of how clonal M. oryzae populations can constantly adapt to novel host germplasm in spite of only harboring limited genetic variation.I hypothesize that genetic material such as virulence factors can be horizontally transferred among M. oryzae strains through mini-chromosomes. I further hypothesize that these small (500kb - 3Mb) supernumerary chromosomes, which act as horizontal gene shuttles, are important determinants of clonal adaptation in M. oryzae. Recent observations by the host laboratory revealed the presence of a mini-chromosome of unknown origin in a clonal rice-infecting M. oryzae strain. This “alien” mini-chromosome displays low sequence similarity to rice blast fungus strains and is most similar to those infecting non-cultivated grasses. M. oryzae strains infecting non-cultivated grasses physically co-occur with rice-infecting M. oryzae strains in the field, suggesting that is where the alien mini-chromosome sequence originates from. In addition, the alien mini-chromosome carries a high number of known and predicted novel virulence genes, indicating it can impact host disease.I will build on these exciting findings and establish the first case of horizontal mChr transfer between plant pathogenic fungi in the field. I will pursue two objectives i) establish the origin of the alien mini-chromosome and ii) determine its impact on virulence to the host. I will accomplish these two objectives using a combination of comparative genomic, fungal genetic and plant pathology approaches.At the completion of this proposal, I will have demonstrated that not only does horizontal mini-chromosome transfer occur in the field, but that it is a driver of host adaptation in the blast fungus.

• DFG Programme: WBP Fellowship
• International Connection: United Kingdom
• Host: Professor Sophien Kamoun, Ph.D.