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Title: Proteolysis of the barley receptor-like protein kinase Rpg1 by a proteasome pathway is required for Rpg1 mediated stem rust resistance

Author
item NIRMALA, J - WASHINGTON STATE UNIV
item DAHL, S - UNIV OF MINN
item STEFFENSON, B - UNIV OF MINN
item KANNANGARA, C - WASHINGTON STATE UNIV
item VON WETTSTEIN, D - WASHINGTON STATE UNIV
item Chen, Xianming
item KLEINHOFS, A - WASHINGTON STATE UNIV

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2007
Publication Date: 6/1/2007
Citation: Nirmala, J., Dahl, S., Steffenson, B., Kannangara, C.G., Von Wettstein, D., Chen, X., Kleinhofs, A. 2007. Proteolysis of the barley receptor-like protein kinase Rpg1 by a proteasome pathway is required for Rpg1 mediated stem rust resistance. PNAS 104:10276-10281.

Interpretive Summary: In plants, disease resistance mediated by the gene-for-gene mechanism involves the recognition of specific molecules produced by the pathogen either directly or indirectly by the resistance gene products. This recognition triggers a series of signals that serve as a molecular switch in regulating a series of defense mechanisms by the plants. In order to understand the mechanism of action with the stem rust resistance gene Rpg1 in barley, we investigated the fate of the resistance gene protein in response to infection with the stem rust fungus. The investigations revealed that the resistance gene protein disappears to undetectable limits only in the infected tissues in response to infection with avirulent, but not with virulent strains. The protein disappearance is very rapid and appears to be due to specific protein degradation through the proteosome-mediated pathway as indicated by inhibition with the proteosome inhibitor MG132, but not by protease inhibitors. Some loss of function mutants that are susceptible to infection with the stem rust fungus fail to degrade the resistance gene protein while others still do so. Thus, the disappearance of the resistance protein is required, but not sufficient, for the disease resistance pathway. The results are useful in understanding mechanisms of rust resistance.

Technical Abstract: In plants, disease resistance mediated by the gene-for-gene mechanism involves the recognition of specific effector molecules produced by the pathogen either directly or indirectly by the R-gene products. This recognition triggers a series of signals thereby serving as a molecular switch in regulating an elaborate series of defense mechanisms by the plants. In order to understand the mechanism of action with the stem rust resistance gene Rpg1 in barley, we investigated the fate of the RPG1 protein in response to infection with the stem rust fungus, Puccinia graminis f. sp. tritici. The investigations revealed that RPG1 disappears to undetectable limits only in the infected tissues in response to infection with avirulent, but not with virulent pathotypes. The RPG1 protein disappearance is very rapid and appears to be due to specific protein degradation via the proteosome-mediated pathway as indicated by inhibition with the proteosome inhibitor MG132, but not by protease inhibitors. Some loss of function Rpg1 mutants that are susceptible to infection with Puccinia graminis f.sp. tritici fail to degrade RPG1 while others still do so. Thus, the disappearance of RPG1 is required, but not sufficient, for the disease resistance pathway.