Project Leader, Organisation
Anne Sawyer, University of Queensland
Objective 4.3 of the National Myrtle Rust Action Plan (MRAP) is to explore methods for resistance and control. Controls for agricultural pathogens e.g. resistant cultivars or fungicides, are inapplicable against myrtle rust in natural environments. RNA interference (RNAi) vaccines are an emerging crop protection platform effective against agricultural pathogens, including wheat and soybean rusts. RNA is sprayed onto plants to trigger RNAi, silencing genes of the targeted pathogen. This project will explore RNAi vaccines as a novel control for myrtle rust in natural populations of Decaspermum humile and Syzygium hodgkinsoniae (both Very High priority species, Objective 4.3.5 MRAP).
Objectives and impact
RNAi vaccines are a novel crop protection strategy with applicability in natural environments. Pathogen-specific double-stranded RNA (dsRNA), which is applied then absorbed by plants and/or pathogens, triggers RNAi silencing pathways on targeted genes. We plan to develop RNAi vaccines as a control for myrtle rust addressing four specific aims:
1: Develop dsRNAs targeting essential Austropuccinia psidii genes
2: Test the effectiveness of synthesised dsRNAs against Austropuccinia psidii
3: Investigate the uptake and movement of dsRNA in the plant and pathogen
4: Deliver an RNAi vaccine against myrtle rust
dsRNAs will be designed to target A. psidii genes ensuring there is no off-target complementarity. Established bioassays and qPCR will be used to test RNA absorption by the plants and pathogen, efficacy of the targets and dose required for gene silencing. Uptake and movement of dsRNA in the plant and pathogen will be monitored using fluorescently-labelled dsRNA. Our preliminary work has found that A. psidii contains RNAi machinery and can take-up dsRNA, suggesting that RNAi vaccines could be effective.
This project uses new technology for plant resistance to protect Very High priority Australian species (NMRAP), with long-term benefits for conservation and biodiversity.
The team provided this update in June 2021, showing really positive results.
We have established artificial leaf assays, as well as detached leaf and whole plant bioassays in Syzygium jambos. We have demonstrated dsRNA uptake by Austropuccinia psidii and have identified a number of A. psidii-specific dsRNAs that inhibit A. psidii urediniospore germination leading to a reduction in disease on detached leaves and whole plants. The next stage of the project is to assess gene knockdown by quantitative reverse transcription PCR (qRT-PCR), examine dsRNA uptake and movement in host plants, investigate the longevity of protection and test the most effective RNA vaccines on Decaspermum humile and Syzygium hodgkinsonia.
Links, outcomes, and more so far!
Project achievements/impacts/outcomes include:
• Completion of Honours project ‘RNA interference-mediated control of the plant-pathogenic rust fungus, Austropuccinia psidii’ by Rebecca Degnan who received First Class Honours.
• Back from the Brink Film Season 3 Episode 4 – Angle-stemmed Myrtle, Dec 16 2020
• Back from the Brink Podcast Episode 9 – The race against the rust, Dec 21 2020
• Presentation of the work at the National Myrtle Rust Symposium, Ballina 23-25 March 2021
• Presentation of the work in the Beyond Myrtle Rust Webinar Series, 12 May 2021
• New collaboration with Scion, New Zealand, who are interested in the potential of RNA vaccines to treat myrtle rust and Phytophthora pine disease