Poster Presentation Australasian RNA Biology and Biotechnology Association 2026 Conference

Insights into Transposable Element taming in Austropuccinia psidii  (#140)

Sebastian N Orellana-Quinteros 1 , Stephen Fletcher 1 , Zhenyan Luo 2 , Benjamin Schwessinger 2 , Peter Crisp 1 , Anne Sawyer 1
  1. The University of Queensland, St Lucia, QUEENSLAND, Australia
  2. Division of Plant Science, Australian National University, Canberra, ACT, Australia

Austropuccinia psidii is an invasive fungal pathogen that infects plants of the Myrtaceae family causing the devastating disease myrtle rust and disrupting fragile biodiversity hotspots. A unique feature of the pandemic A. psidii biotype that is present in Australia is its extremely broad host range compared to other members of the Pucciniales order of rust fungi (Aime & McTaggart, 2021). This is thought to have arisen from A. psidii’s ~ 1 Gb haploid genome comprising of >90% transposable elements (TEs) content (Luo et al., 2026; Tobias et al., 2021). This burst of TEs likely drives virulence gene evolution and therefore, understanding how TE enriched regions are regulated is crucial for developing lasting disease management strategies. Double-stranded RNA (dsRNA) biopesticides have shown great promise to prevent and cure myrtle rust, however, the exact molecular pathway of dsRNA-mediated disease protection in A. psidii remains unclear (Degnan., et al., 2023; Degnan., et al., 2023). We are investigating whether dsRNA treatment of A. psidii spore affects DNA methylation and the mechanisms of TE regulation. Upon integrating Argonaute loaded small RNA sequencing (sRNA) and long-read 5-methylcytosine (5mC) (CpG) data, evidence for an RNA-directed DNA methylation-like (RdDM-like) pathway in asexual urediniospores has become apparent due to distinct sRNA and 5mC co-occurrence enrichment globally and at young TE body flanks. Despite being the most abundant infectious spore stage, urediniospores only capture a slice of TE regulation and sRNA dynamics within the A. psidii lifecycle. We are next interested in expanding our DNA methylation analyses into CHG and CHH context 5mC patterns in all A. psidii spore stages and again co-analysing sRNA sequencing data to reveal potential spore-stage-specific co-occurrence. This research has and will continue to inform fundamental questions surrounding TE taming in A. psidii.

  1. Aime, M. C., & McTaggart, A. R. (2021). A higher-rank classification for rust fungi, with notes on genera. Fungal Systematics and Evolution, 7(1), 21–47. https://doi.org/10.3114/fuse.2021.07.02
  2. Degnan, R. M., McTaggart, A. R., Shuey, L. S., Pame, L. J. S., Smith, G. R., Gardiner, D. M., Nock, V., Soffe, R., Sale, S., Garrill, A., Carroll, B. J., Mitter, N., & Sawyer, A. (2023). Exogenous double-stranded RNA inhibits the infection physiology of rust fungi to reduce symptoms in planta. Molecular Plant Pathology, 24(3), 191–207. https://doi.org/10.1111/mpp.13286
  3. Degnan, R. M., Shuey, L. S., Radford-Smith, J., Gardiner, D. M., Carroll, B. J., Mitter, N., McTaggart, A. R., & Sawyer, A. (2023). Double-stranded RNA prevents and cures infection by rust fungi. Communications Biology, 6(1), 1234. https://doi.org/10.1038/s42003-023-05618-z
  4. Luo, Z., Tobias, P. A., Singh, L., Dong, C., Martino, A. M., Saber, E., Quecine, M. C., Massola, N. S., Jr, Amorim, L., Zhang, P., Li, J., Singh, S., Zhang, Z., Jones, A., Park, R. F., Schwessinger, B., Edwards, R. J., & Boufleur, T. R. (2026). Host adaptation and genome evolution of the broad host range fungal rust pathogen, Austropuccinia psidii. G3 (Bethesda, Md.), 16(1), jkaf255. https://doi.org/10.1093/g3journal/jkaf255
  5. Tobias, P. A., Schwessinger, B., Deng, C. H., Wu, C., Dong, C., Sperschneider, J., Jones, A., Lou, Z., Zhang, P., Sandhu, K., Smith, G. R., Tibbits, J., Chagné, D., & Park, R. F. (2021). Austropuccinia psidii, causing myrtle rust, has a gigabase-sized genome shaped by transposable elements. G3 (Bethesda, Md.), 11(3). https://doi.org/10.1093/g3journal/jkaa015