Melaleuca quinquenervia; a model for investigating the genetic basis of resistance to Austropuccinia psidii

Abstract

Austropuccinia psidii is a biotrophic fungal pathogen known to infect species within the family Myrtaceae. Originating in South America, it was first detected in the state of New South Wales in Australia in 2010. By 2022, it had spread to all states and Territories aside from South Australia. Unlike other rust fungi, A. psidii has a broad host range, with the global host list exceeding 480 Myrtaceae species. While extensive, host responses range from highly susceptible to highly resistant within and between species, providing an opportunity to investigate the genetic basis of this differential phenotype. To date, studies investigating the genetic basis of resistance to A. psidii have been conducted on many different host species. The following research established Melaleuca quinquenervia as a model organism for studying the genetic basis of resistance to A. psidii, as it displays a range of phenotypic responses upon exposure to the pathogen. The generation of a high-quality genome for M. quinquenervia revealed a large expansion of the nucleotide binding site leucine-rich repeat (NLR) family of disease resistance genes. Transcriptomic analyses of the A. psidii-challenged progeny of the tree used for the generation of the genome sequence revealed upregulation of several of these putative disease resistance genes. Genotyping and expression analyses showed the conservation and expression of these genes across Melaleuca species, indicating a functional role in pathogen defence. It is anticipated that this research will provide a valuable resource for investigating the genetic basis of resistance to A. psidii in other Myrtaceae species.