Wheat blast fungus can re-arrange genetic components between its seven main chromosomes and extra mini-chromosomes. That enables it to defeat a wheat plant’s resistance, according to researchers at Kansas State University.

The fungus uses its disease-causing proteins called “effectors.” The fungus also stores those effectors for later use in reducing a plant’s defenses and causing disease, said Barbara Valent, a professor of plant pathology at Kansas State University.

The fungus produces hundreds of small effectors. In some cases plants recognize individual effectors and trigger resistance to block infection. But the fungus overcomes that resistance by eliminating the offending effector gene.

“Before we started the project we knew some effector genes could move,” said Sanzhen Liu, an associate professor of plant pathology at Kansas State University. “But typically they’d move to the ends of main chromosomes. It’s surprising they carry fragments to mini-chromosomes. The mini-chromosomes serve as reservoirs for effector genes. The fungus employs some strategy through the mini-chromosome to gain advantage.”

Valent said, “Our group discovered the only effective resistance gene that's protecting wheat in the field right now. Earlier strains weren’t aggressive on wheat. Strains causing disease now are extremely aggressive. The fungus has worsened and there’s potential for it to become even worse. We need to better understand the mechanism by which the fungus re-arranges effector genes to learn how to intervene. Maybe we can find genes that aren’t so easily deleted.”

The researchers have found a few effector genes that don’t seem to be part of the fungus arsenal. While the researchers are screening for greater resistance, they’re not finding many useful resistance genes. Visit www.k-state.edu/wheatblast for more information.

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