Interspecific Gene Exchange Introduces High Genetic Variability in Crop Pathogen

Area of Science:

• Evolutionary Biology
• Genomics
• Mycology

Background:

• Hybridization and introgression are recognized drivers of eukaryote evolution.
• The specific impact of recurrent introgression on fungal evolution remains largely unexplored.
• Zymoseptoria tritici is a significant fungal pathogen of wheat, making its evolutionary dynamics crucial to understand.

Purpose of the Study:

• To investigate the distribution and impact of recurrent introgression across the genome of the fungal wheat pathogen Zymoseptoria tritici.
• To differentiate introgressed regions from those shaped by incomplete lineage sorting.
• To identify genes and genomic features affected by introgression, including potential virulence factors and transposable elements.

Main Methods:

• Comparative population genomics using genome data from five Zymoseptoria species.
• Analysis of genome-wide introgression signatures and haplotype patterns.
• Window-based phylogenetic analyses to assess region origins.
• Comparison of observed and expected haplotype block lengths to rule out incomplete lineage sorting.

Main Results:

• Introgressed regions constitute 5% of the Z. tritici genome, overlapping with over 1,000 genes.
• Phylogenetic analyses confirmed introgression as the source of non-monophyletic genomic regions.
• Eighteen putative virulence determinants were identified within introgressed regions.
• Introgressed regions showed an enrichment of transposable elements, suggesting a role for hybridization in their spread.
• Similar introgression patterns were observed in the related species Zymoseptoria ardabiliae.

Conclusions:

• Recurrent hybridization has a substantial impact on the genome evolution of Z. tritici.
• Hybridization contributes to the acquisition of potentially adaptive genes, including virulence factors.
• Hybridization may facilitate the spread of transposable elements within fungal genomes.
• Widespread hybridization is likely a common evolutionary mechanism in closely related grass pathogens like Zymoseptoria species.