Martino, A. M. | bioRxiv Science

bioRxiv2023

Screening of Threatened and Priority listed Melaleuca species from Western Australia reveals high susceptibility to Austropuccinia psidii in controlled inoculations

Austropuccinia psidii causes rust disease on species within the family Myrtaceae and was first detected in Australia in 2010, with the first detection in Western Australia in 2022. While species within the genus Melaleuca from Eastern Australia show variable responses to the pathogen, little is known of the response of species from Western Australia. This study established that 13 previously unscreened species of Melaleuca, including Threatened and Priority species that were grown from seeds sourced from Western Australian populations, were susceptible to the pandemic strain of the pathogen. The proportion of highly susceptible plants within a single species ranged from 2% - 94%, with several species displaying highly variable levels of resistance to A. psidii. These results highlight the importance of disease screening and may direct conservation efforts.

plant biology↗

bioRxiv2023

A high-quality pseudo-phased genome for Melaleuca quinquenervia shows allelic diversity of NLR-type resistance genes

BackgroundThe coastal wetland tree species Melaleuca quinquenervia (Cav.) S.T.Blake (Myrtaceae), commonly named the broad-leaved paperbark, is a foundation species in eastern Australia, Indonesia, Papua New Guinea, and New Caledonia. The species has been widely grown as an ornamental, becoming invasive in areas such as Florida in the United States. Long-lived trees must respond to a wide range pests and pathogens throughout their lifespan, and immune receptors encoded by the nucleotide- binding domain and leucine-rich repeat containing (NLR) gene family play a key role in plant stress responses. Expansion of this gene family is driven largely by tandem duplication, resulting in a clustering arrangement on chromosomes. Due to this clustering and their highly repetitive domain structure, comprehensive annotation of NLR encoding genes within genomes has been difficult. Additionally, as many genomes are still presented in their haploid, collapsed state, the full allelic diversity of the NLR gene family has not been widely published for outcrossing tree species. ResultsWe assembled a chromosome-level pseudo-phased genome for M. quinquenervia and describe the full allelic diversity of plant NLRs using the novel FindPlantNLRs pipeline. Analysis reveals variation in the number of NLR genes on each haplotype, differences in clusters and in the types and numbers of novel integrated domains. ConclusionsWe anticipate that the high quality of the genome for M. quinquenervia will provide a new framework for functional and evolutionary studies into this important tree species. Our results indicate a likely role for maintenance of NLR allelic diversity to enable response to environmental stress, and we suggest that this allelic diversity may be even more important for long-lived plants.

genomics↗

bioRxiv2022

Three species of Melaleuca from Western Australia are highly susceptible to Austropuccinia psidii in controlled inoculations

Austropuccinia psidii, the fungus causing myrtle rust, was detected in Western Australia for the first time in June 2022. Few Western Australian plant species have been screened for response to the pathogen. Melaleuca thyoides, Melaleuca marginata and Melaleuca leucadendra grown from seeds sourced from Western Australian populations were all highly susceptible to an isolate of the pathogen from eastern Australia.

plant biology↗