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Sanctuary: a Starship transposon facilitating the movement of the virulence factor ToxA in fungal wheat pathogens

Summary

Researchers found that a disease-causing gene called ToxA, which helps fungal pathogens infect wheat crops, travels between different fungal species using molecular ‘cargo ships’ called Starship transposons. By sequencing multiple fungal isolates, scientists discovered that ToxA rides within a larger mobile genetic element called Sanctuary that can move around within fungal genomes and between species. This discovery helps explain how wheat pathogens become more dangerous over time through horizontal gene transfer.

Background

The ToxA virulence gene is found in three fungal wheat pathogens (Parastagonospora nodorum, Pyrenophora tritici-repentis, and Bipolaris sorokiniana) and is horizontally transferred between species via mobile genetic elements. Previous studies identified the 14 kbp ToxhAT transposon carrying ToxA, but questions remain about its activity and broader genomic context.

Objective

To confirm the active transposition of ToxhAT in B. sorokiniana isolates using long-read sequencing and to characterize the larger mobile genetic element in which ToxhAT is embedded. The study aims to understand the mechanisms of horizontal gene transfer of virulence factors among fungal wheat pathogens.

Results

ToxhAT was found to be an active transposon with a 2 bp ‘TA’ target site duplication, indicating it is a Tc1/Mariner-type transposon (renamed ToxTA). ToxTA is embedded within a larger 170-196 kbp Starship transposon named Sanctuary, which contains multiple haplotypes and accessory genes. ToxTA has been independently acquired by two different Starships (Sanctuary and Horizon) in different fungal species, demonstrating convergent capture of virulence genes.

Conclusion

This work demonstrates that Sanctuary and Horizon are active Starship transposons facilitating horizontal transfer of the virulence factor ToxA among fungal wheat pathogens. The independent acquisition of ToxTA by two distinct Starships in multiple fungal species highlights how transposon-mediated horizontal gene transfer drives pathogen evolution and emergence.
  • Published in:mBio,
  • Study Type:Genomic and Bioinformatics Study,
  • Source: 40905677
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