Stealth pathogen’s secrets exposed

U. WARWICK (UK) — Scientists have sequenced the genome of the “stealth bomber” of plant pathogens, discovering how it is able to sneak past a plant’s immune defenses.

The findings are expected to provide tools to identify immunity components and to devise new ways to prevent disease.

For the study, published in the journal Science, researchers looked at an obligate biotroph, a type of plant pathogen that has adapted so exquisitely to its host that it extracts nutrients only from living plant tissue and cannot grow away for their plant.

While the organism may once have been able to exist by itself it has now evolved in such a way that it cannot survive without a host plant and usually that has to be a very specific type of host plant.

Hyaloperonospora arabidopsidis can only survive on its host the model plant Arabidopsidis, the model plant  of the plant science world.

The pathogen is a type of water mold that causes yellow patches and fuzzy white mold on leaves. Close relatives cause disease and damage on many crops including broccoli, maize, grapes and lettuce.

The researchers found that this particular plant pathogen has evolved a highly successful strategy that allows it to present a very small profile to its host plant disease prevention defenses.

Hyaloperonospora arabidopsidis is able to minimize the number of genetic markers it carries that could be picked up by a plant’s defences and seen as a threat because it is able to lose, or never acquire in the first place, many abilities found in other pathogens.

“Hyaloperonospora arabidopsidis is one of the stealth bombers of the world of plant pathogens.,” says Jim Beynon, professor of life sciences at the University of Warwick.

“We can see much of how it has actually slimmed down some key elements of its genetic material in order to get around the plant’s natural defenses—essentially by stealth.”

To exploit the pathogen’s arsenal to mount their own sneak assault on other challenging plant pathogens, researchers used the “RXLR effectors,” Beynon says.

Pathogens use a large armory  of RXLR effectors to suppress the mechanisms used by plants to detect and then block pathogens. Although having a slimmed down stealth profile, yaloperonospora arabidopsidis still maintains 134 RXLR effectors in its armory.

Understanding the role of these effectors will be the key direction of future research.

Researchers say that while this approach may help Hyaloperonospora arabidopsidis in its stealth attack, it also opens up a major opportunity for researchers to gain insights across a vast range of plant pathogens.

“This research provides a new window into how Hyaloperonospora arabidopsidis has slimmed down key elements of its genetic material to avoid the plant’s natural defenses,” Beynon says.

“Despite this reduction, amazingly, it still sends over 100 proteins into plant cells to suppress the immune responses. Understanding how these proteins suppress plant immunity will enable us to select disease resistant crop plants and combat plant disease such as potato blight and sudden oak death.

“Losses to disease in food crops can be very significant and to feed a growing population set to reach 9 billion by 2050 we need to increase food production. Reducing losses because of disease will be an important part of this.”

Researchers from Virginia Polytechnic Institute and State University (Virginia Tech) contributed to the study.

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