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Destroy Darth Vader and the “resistance” will win (disease resistance, that is)

Darth Vader walks into a room…. *Heavy breathing*.

“Stormtroopers, find Luke Skywalker and kill him.”

“Yes Master,” the Stormtroopers all say, and immediately jostle aboard their spaceship on their mission.

Unfortunately for Darth Vader, his Stormtroopers couldn’t get past the small, cute and cuddly Ewoks or even a blind man with a stick, even though they were armed with blaster rifles. However, if they had succeeded to kill Luke, that would be the end of the Star Wars Saga. Nooo!

Here at CCDM, we’re also in the middle of a Star Wars Saga in our fight against wheat diseases yellow spot and septoria nodorum blotch, but unlike the real Star Wars, this is a saga that we do want to end.

We believe we have discovered the “Darth Vader” in both diseases – the gene that commands other genes to infect wheat and cause disease. The “master gene” (Darth Vader) that command “effectors” (Stormtroopers).

Up until now, CCDM’s main game has been to discover “effector genes” that produce toxic proteins that kill wheat cells, which the fungus then infects and feeds on.

But there are many effectors that take different forms in many diseases and, according to CCDM’s Kasia Clarke, the process of finding effectors can be extremely time consuming.

“By discovering the master gene that commands effector genes that help to cause disease, we have potential to cut some serious corners on the path to breeding disease resistant wheat,” she said.

“This discovery has potential to go beyond septoria nodorum blotch and yellow spot too, to other necrotrophic diseases such as net blotches of barley – this could be a real game changer for disease resistance breeding in cereals.”

An idea that sprung from cabbage

Just a couple of years ago, the team got wind of a discovery from a Korean and US research team who found a master gene in the devastating cabbage fungal disease, dark leaf spot.

When they deleted this master gene from the pathogen in the lab, the pathogen was not able to cause disease symptoms on cabbage leaves any more. They suggested that the gene they deleted may function as a switch that regulates effector-like-genes.

With a project team behind her, Kasia set out to discover the same gene within septoria nodorum blotch and yellow spot. By doing a simple search on the two genomes, they found the gene that is equivalent to the cabbage disease master gene.

Can what’s been done in cabbage disease be done in wheat disease?

The team took a sample of both wheat pathogens and deleted the master gene from them.

“When we infected wheat with the mutant septoria nodorum blotch fungus, we noticed two out of three major effectors were not damaging the wheat as they normally do,” Kasia said.

“This means without the master gene, the pathogen abolishes its ability to produce toxic effectors ToxA and Tox3, and perhaps others.

“It’s the same with yellow spot mutants. When you take away the master gene, the mutant fungi struggle to infect, and necrosis (cell death) is not visible on leaves.”

Caption: Leaves of a wheat variety that that would normally be affected by septoria nodorum blotch and yellow spot effectors

What does this mean for breeding disease resistant wheat?

Kasia said if they can figure out the signal that activate the pathogen’s master gene to crack the whip, they essentially formulate strategies to shut it down. According to Kasia, this next step shouldn’t be too far away.

“The future is exciting for genetic resistance in cereals, not just for yellow spot and septoria nodorum blotch, but for other diseases such as barley net blotch. Most pathogens that live a necrotrophic lifestyle are likely to have an easy-to-find master gene that regulates effector production.”

Stay tuned for Episode 2…

Read more about it in the paper

This research was recently published as an open access article in Molecular Plant Pathology, and can be found here: http://onlinelibrary.wiley.com/doi/10.1111/mpp.12511/abstract

For more information about the research please contact Dr Kar-Chun Tan, E: Kar-Chun.Tan@curtin.edu.au, T: +61 8 9266 9916.

About Kasia Clarke

Kasia is a senior research officer in CCDM’s Septoria Nodorum Blotch program. She has been working on fungal pathogens for the past 14 years, helping to improve disease resistance in wheat for Australian growers.

In 2014 she was part of the team that were finalists in the Eureka Awards for their work in developing and commercialising Effector Kits for infiltration onto wheat leaves, to ultimately speed up the breeding process.

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