Communication between barley-plant and stem rust spore

John Bakum
Friday, October 21, 2011

Andris Kleinhofs and Jayaveermuthu Nirmala

In a paper published in the Proceedings of the National Academy of Sciences, USA (PNAS), Nirmala et al. 108:14676-14681, (2011) describe the isolation and preliminary characterization of two effector proteins that coordinately induce stem rust resistance gene protein product RPG1 to become phosphorylated and initiate disease resistance signaling. The quest for these proteins started with an earlier discovery that Puccinia graminis f. sp. tritici spores initiate RPG1 phosphorylation within 5 minutes of landing on the leaf surface (Nirmala et al., Mol. Plant-Microbe Interact. 23:1635-1642, 2010). This discovery was astounding and indicated that the effectors are already present on the spore surface and that the plant has an early warning system to indicate that the enemy has landed.

Andy Kleinhofs and Jayaveeramuthu Nirmala. Photo credit: Brian Clark/Washington State University
Andy Kleinhofs and Jayaveeramuthu Nirmala.
Credit: Brian Clark/Washington State University
While this discovery is primarily of basic interest to scientists working with plant-pathogen interactions, it addresses the question how rusts initiate disease and plants with the appropriate resistance genes initiate resistance. Such basic understanding of how rusts work will provide clues for developing strategies to fight them. We already know that the rust spores must attach themselves to the leaf surface to initiate their work and such attachments are inhibited by the simple tripeptide RGD. Can RGD peptide be exploited to stop other rust spores? We do not know yet, but we are working to find out. We already know that the effector proteins we isolated from Avirulent rust races are also present in Virulent races such as Ug99, but in modified form. Perhaps these modified effector proteins play a virulence role or activate other resistance genes. These and other questions, such how do these effector proteins initiate their signaling so rapidly, are being investigated by us and in collaboration with Dr. Les J. Szabo at USDA ARS Cereal Disease Laboratory and Dr. Brian J. Steffenson at the University of Minnesota.

More Information:

Concerted action of two avirulent spore effectors activates Reaction to Puccinia graminis 1 (Rpg1)-mediated cereal stem rust resistance published in the Proceedings of the National Academy of Sciences

Washington State University Press Release