Meet the new enemy of invasive myrtle rust: RNA

The invasive fungus myrtle rust might have met its match.

Myrtle rust has been damaging hundreds of Australian plants since its introduction in 2010. It has a devastating impact on plants in the Myrtaceae family – including eucalyptus trees, lilly pilly, and bottle brush.

But a team of scientists has a new way to stop its spread: RNA, and some water.

The researchers, from the University of Queensland (UQ) and the state Department of Agriculture and Fisheries, have developed a type of RNA that triggers a self-destruct sequence in myrtle rust.

The RNA could protect healthy plants from being infected and let plants recover even after they’d been infected for 2 weeks.

Leaves with yellow fungal infection
Leaves infected with myrtle rust. Credit: Megan Pope, UQ

While the team has previously seen success with RNA that stops pest infestations, Rebecca Degnan, a PhD candidate at UQ, says that this is the first time the team has been able to cure an infection.

Degnan tells Cosmos that the “RNA is designed to target genes that the fungus needs to survive”.

It triggers an RNA interference, or RNAi, mechanism: a gene silencing process.

“We target barcoding genes, which are genes that are very highly expressed and essential, but they also have regions that are very specific to each species,” says Degnan.

“So we’ll target a section of that gene that is specific to myrtle rust and myrtle rust alone.”

The researchers mix the RNA with water and spray it on the leaves of vulnerable plants. In greenhouse-based experiments, this protected the plants from fungus and improved their health for at least 6 weeks post infection.

Two people standing in greenhouse holding plants and smiling
RNA researchers Dr Anne Sawner and Rebecca Degnan in the greenhouse. Credit: Megan Pope, UQ

RNA, unlike DNA, is typically a single strand of genetic information. But this process uses double-stranded RNA.

“Double stranded RNA is typical of some viruses,” explains Degnan.

“One hypothesis is that this RNAi pathway evolved in eukaryotes as a defence mechanism against viruses. So genomes evolved this mechanism to protect themselves from genome invaders.”

The researchers are keen to take their treatment to field trials.

“Field trials [will help] to see what happens when you have when you have other factors in play, like plants from the natural environment,” says Degnan.

“The idea will be that eventually, it could be used in a more applied sense – maybe in the nursery industry, in ex situ conservation in Myrtaceae plantations, or even for the treatment of individual important trees.

“It’s obviously a long process. But that’s the ideal outcome.”

A paper describing the research was published in Communications Biology.

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