Skip to main content
ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Disease and Pest Management Research Unit » Research » Publications at this Location » Publication #426590
Research Project: Knowledge Based Tools for Exotic and Emerging Diseases of Small Fruit and Nursery Crops

Location: Horticultural Crops Disease and Pest Management Research Unit

Title: The poplar pathogen Sphaerulina musiva has a dynamic genome architecture marked by chromosomal inversions and changes in transposable element abundance

Author
item ZACCARON, ALEX - Oregon State University
item LASSAGNE, ALEXANDRE - Oregon State University
item SONDRELI, KELSEY - Oregon State University
item SUDERMANN, MARTHA - Oregon State University
item ALCALA BRISENO, RICARDO - Oregon State University
item Grunwald, Niklaus
item WEISBERG, ALEXANDRA - Oregon State University
item LEBOLDUS, JARED - Oregon State University

Submitted to: Microbial Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2025
Publication Date: 1/7/2026
Citation: Zaccaron, A.Z., Lassagne, A., Søndreli, K.L., Sudermann, M.A., Alcalá Briseño, R.I., Grünwald, N.J., Weisberg, A.J., LeBoldus, J.M. 2026. The poplar pathogen Sphaerulina musiva has a dynamic genome architecture marked by chromosomal inversions and changes in transposable element abundance. Microbial Genomics. 12(1):001603. https://doi.org/10.1099/mgen.0.001603.
DOI: https://doi.org/10.1099/mgen.0.001603

Interpretive Summary: Poplar trees are a valuable source of fiber and other wood-based products. However, they are often susceptible to Sphaerulina musiva, a fungal pathogen causing Septoria leaf spot and stem canker disease. The domestication and expansion of poplar cultivation facilitated the movement of S. musiva to western North America, giving rise to new lineages of the pathogen that co-evolve with native hosts. This research examines the genetic diversity of S. musiva populations and how they evolved in order to improve our understanding of pathogen incursions and how they genetically adapt to new environments. These findings greatly expand our understanding of fungal plant pathogen evolution which will aid in developing adaptive responses to introduced pathogens in the future.

Technical Abstract: Fungal plant pathogens possess dynamic genomes, frequently shaped by transposable elements, that enable rapid adaptation to adverse conditions and host resistance mechanisms. However, assessing the adaptive significance of these genomic features remains challenging, in part due to the lack of high-quality genome assemblies for multiple members of a given species. To gain insights into genomic factors shaping pathogen evolution, we sequenced and assembled near-chromosome scale genomes of 18 geographically diverse North American isolates of Sphaerulina musiva, a significant, important pathogen causing Septoria leaf spot and stem canker disease of poplar trees. Comparative genomic analyses indicated that all isolates possess 13 chromosomes with no evidence of accessory chromosomes. Transposable element (TE) content varied considerably among isolates (6.8% to 15.7%), with a higher abundance in isolates from Oregon, British Columbia, and Alberta, geographic regions outside the native range of S. musiva. The variation in TE content largely explained differences in genome size among isolates, and suggested lineage-specific proliferation of TEs. Although a gene-based pangenome analysis indicated a relatively low percentage (9.5%) of accessory genes, this subset was enriched for candidate effectors. Our results indicate that S. musiva exhibits features of a “one-speed genome” model. However, increased TE content is correlated with longer intergenic regions of candidate effector genes, suggesting that proliferation of TEs may be driving increased compartmentalization. Finally, synteny analysis revealed a total of 43 long chromosomal inversions with average size of 293 kb that covered 34% of the S. musiva genome. These chromosomal inversions were more frequently observed in isolates from the pathogen’s native range in the Eastern USA, and at least one inversion was predicted to affect the organization of a secondary metabolite gene cluster. These findings provide novel insights into the genome structure, TE dynamics, and chromosomal rearrangements of the poplar pathogen S. musiva, offering a foundation for understanding its evolution and adaptation across diverse geographic regions and host species.