Host adaptation and genome evolution of the broad host range fungal rust pathogen, Austropuccinia psidii

Sep 29, 2026

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Rust diseases on plants are caused by fungi in the order Pucciniales. Typically, rust fungi have narrow host specificity, yet the pandemic biotype of Austropuccinia psidii infects over 480 myrtaceous species globally. A fully phased, chromosome-level genome assembly was generated to examine infection biology, including conserved 18-chromosome karyotypes and reassortment producing 19/17 chromosomes.

LanguageEnglish

CategoryResearch & Report

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Pages21

Reading Time53 min

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Abstract

Introduction

G3, 2026, 16(1), jkaf255 [https://doi.org/10.1093/g3journal/jkaf255](https://doi.org/10.1093/g3journal/jkaf255) Advance Access Publication Date: 28 October 2025 Fungal Genetics and Genomics Host adaptation and genome evolution of the broad host range fungal rust pathogen, Austropuccinia psidii Zhenyan Luo , 1 ,† Peri A. Tobias ,2 ,*,† Lavi Singh,1 Chongmei Dong,3 Alyssa M. Martino,2 Elle Saber,1 Maria C. Quecine ,4 Nelson S. Massola Jr. ,4 Lilian Amorim,4 Peng Zhang ,2 Jianbo Li,2 Smriti Singh,2 Ziyan Zhang,1 Ashley Jones , 1 Robert F. Park ,3 Benjamin Schwessinger , 1 ,* Richard J. Edwards,3 ,* Thais R. Boufleur1 ,4 ,* ,† 1Research School of Biology, The Australian National University, Canberra, ACT 2601, Australia 2School of Life and Environmental Sciences, The University of Sydney, Camperdown, NSW 2006, Australia 3School of Life and Environmental Sciences, Plant Breeding Institute, University of Sydney, Cobbitty, NSW 2570, Australia 4Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba, São Paulo 13418-900, Brazil *Corresponding authors: Benjamin Schwessinger, Research School of Biology, The Australian National University, Canberra, Acton ACT 2601, Australia. Email: benjamin. [schwessinger@anu.edu.au](schwessinger@anu.edu.au); Thais R. Boufleur, Department of Plant Pathology and Nematology, Luiz de Queiroz College of Agriculture, University ofSão Paulo, Piracicaba, São Paulo 13418-900, [Brazil. Email: thaisboufleur@usp.br](Brazil. Email: thaisboufleur@usp.br); Peri A. Tobias, School of Life and Environmental Sciences, The University of Sydney, Camperdown, NSW 2006, Australia. Email: [peri.tobias@sydney.edu.au](peri.tobias@sydney.edu.au); Richard J. Edwards, School of Life and Environmental Sciences, Plant Breeding Institute, University of Sydney, Cobbitty, NSW 2570, Australia. Email: [rich.edwards@uwa.edu.au](rich.edwards@uwa.edu.au)[ ](rich.edwards@uwa.edu.au)†Equal contributions. Abstract Rust diseases on plants are caused by fungi in the order Pucciniales. Typically, rust fungi have narrow host specificity however the pandemic biotype of Austropuccinia psidii has an unusually broad host range causing disease on over 480 myrtaceous species globally. We assembled and analyzed a fully phased chromosome-level genome for the pandemic A. psidii and addressed key outstanding questions of its infection biology. Our research revealed a conserved rust fungal karyotype of 18 haploid chromosomes, in line with fungi for distantly related cereal rusts. We observed chromosomal re-assortment between the 2 nuclei, with one nucleus carrying 19 and the other 17 chromosomes. The synteny of universal single-copy orthologs is mostly maintained with the distantly related rust fungus Puccinia graminis f. sp. tritici. In contrast, nucleotide composition and methylation profiles ofA. psidii are distinct compared to rust fungi with smaller genome sizes that have not undergone massive transposable element expansions. Our analysis of MAT loci supports a tetrapolar mating system for A. psidii with a novel finding of expanded numbers of pheromone peptide precursors. We show that infection dynamics of A. psidii are consistent on 4 different susceptible host species separated by 65 mya of evolution and that transcriptional regulation during infection reveals 2 distinct waves of gene expression in early and late infection, including allele-specific expression of candidate effectors. Together, these findings enhance the understanding of the genome biology and pathology of A. psidii, while also providing a valuable resource for future research on this serious rust pathogen. Keywords: Pucciniales; mating-type; transposable elements; DNA methylation; transcriptome; phased genome assembly Introduction Rust diseases, caused by obligate biotrophic fungi from the order Pucciniales, have historically devastated economies and contributed to famines worldwide (Oliver 2024) . The Pucciniales are one of th

FAQs

Why is Austropuccinia psidii notable among rust pathogens?

The pandemic biotype shows unusually broad host range, causing disease on over 480 myrtaceous species worldwide.

What genome features were found in the pandemic A. psidii?

The study reports a conserved 18 haploid-chromosome karyotype and observes chromosomal reassortment between nuclei, yielding 19 and 17 chromosomes.

How do transcriptional changes during infection behave?

Infection transcription reveals two distinct waves of gene expression during early and late infection, including allele-specific expression of candidate effectors.

Sep 29, 2026

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