Century-Old Rice Blight Finally Toppled? Key to Immunity Discovered

Rice crops have been battling a deadly bacterial blight for over a century - one that decimates crops and can leave entire farms in ruin. Now researchers think that affected regions may finally stand a chance after discovering a rare mechanism that leave some lucky plants resistant to infection.

That's at least according to a study recently published in the journal Science Advances, which details how an international team of researcher finally uncovered the key to Xoo immunity.

Xanthomonas oryzaepv.oryzae, or Xoo, is traditionally characterized by a discoloration on the leaves of young rice plants. It quickly escalates from there, turning the leaves brittle and grey, and rendering them useless in photosynthesis. Starved for energy, affected plants quickly die, sometimes devastating up to 80 percent of a single season's crop. In Japan alone, annual losses are estimated to be between 22,000 and 110,000 tons.

What's worse, this pathogen affects rice in a unique way, rendering industry standards for combating bacterial infection, such as the application of copper compounds or antibiotics, largely ineffective.

That's why researchers have turned to closely analyzing those few plants that were lucky enough - in the wacky roulette of genetics - to wind up with strong resistances to Xoo. (Scroll to read on...)

Only six year ago, modern research practices revealed that immune responses in rice are triggered to battle the blight when a Xoo protein dubbed Ax21 binds to the plants' cellular receptor XA21.

"We were ecstatic with our results in 2009 because identifying the molecule that XA21 recognizes provides an important piece to the puzzle of how the rice plant is able to respond to infection," Pamela Ronald, a plant geneticist for both JBEI and UC Davis, explained in a statement.

It was theorized that once understood. experts could craft a crop (via genetic editing) that could easily shrug off Xoo. However, after a century of researching the blight (historically starting in 1901) could it be that easy? The answer was no.

As it turned out, Ax21 wasn't the savior Ronald and her colleagues thought it was. In fact, it was more like the housemate of the protein they needed. In other words, when Batman was the hero Gotham deserved, the researchers wound up with his butler, Alfred. (Come on guys, nerd out with me for a moment. We're talking about rice pathogens after all).

"We hypothesized that the activator of XA21 might be encoded in the proximity of the molecular machinery that we already knew was involved," added Rory Pruitt, a member of Ronald's research group.

So the researchers kept looking. Now, six years later, they've announced that this time for sure, they have their hero. (Scroll to read on...)

"Our results show that RaxX, a small, previously undescribed bacterial protein, is required for... immunity to Xoo," Ronald happily reported. "XA21 can detect RaxX and quickly mobilize its defenses to mount a potent immune response."

The researchers added that even if the ultimate goal of their work - the development of a fully-immune rice crop - is still a ways away from being realized, the results can still be immediately useful for rice farmers.

During their numerous tests, the team also determined which strains of Xoo are heartier than others, even when running up against plants with the XA21 response.

"Like prescribing the best vaccination for the flu each season by monitoring which flu strains are going to be the most prevalent, it should be possible to screen wild Xoo populations in the rice-growing regions of Asia and Africa for whether they encode alleles that are recognized by XA21," Schwessinger explained. "We can then inform farmers which rice varieties will be resistant to those bacterial populations."

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