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United States Department of Agriculture

Agricultural Research Service

Research Project: CONTROL OF RUSTS OF CEREAL CROPS

Location: Wheat Genetics, Quality Physiology and Disease Research

Title: Stem rust spores elicit rapid RPG1 phosphorylation

Authors
item Nirmala, Jayaveeramuthu -
item Drader, Tom -
item Chen, Xianming
item Steffenson, Brian -
item Kleinhofs, Andris -

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 30, 2010
Publication Date: July 16, 2010
Citation: Nirmala, J., Drader, T., Chen, X., Steffenson, B., Kleinhofs, A. 2010. Stem rust spores elicit rapid RPG1 phosphorylation. Molecular Plant-Microbe Interactions. 23:135-1642.

Interpretive Summary: Stem rust threatens cereal production worldwide. Understanding the mechanism by which durable resistance genes, such as Rpg1, function is critical. We show that the RPG1 protein is phosphorylated within 5 min by exposure to spores from avirulent but not virulent races of stem rust. Transgenic mutants encoding an RPG1 protein with an inactive kinase domain fail to phosphorylate RPG1 in plants and are susceptible to stem rust, demonstrating that phosphorylation is a prerequisite for disease resistance. Protein kinase inhibitors prevent RPG1 phosphorylation and result in susceptibility to stem rust, providing further evidence for the importance of phosphorylation in disease resistance. We conclude that phosphorylation of the RPG1 protein by the kinase activity of the pK2 domain induced by the interaction with an unknown pathogen spore product is required for resistance to the avirulent stem rust races. The pseudokinase pK1 domain is required for disease resistance but not phosphorylation. The very rapid phosphorylation of RPG1 suggests that an effector is already present in or on the stem rust urediniospores when they are placed on the leaf surface. However, spores must be alive, as determined by their ability to germinate, in order to elicit RPG1 phosphorylation. The findings have advanced our understanding of mechanisms of plant resistance to diseases.

Technical Abstract: Stem rust threatens cereal production worldwide. Understanding the mechanism by which durable resistance genes, such as Rpg1, function is critical. We show that the RPG1 protein is phosphorylated within 5 min by exposure to spores from avirulent but not virulent races of stem rust. Transgenic mutants encoding an RPG1 protein with an in vitro inactive kinase domain fail to phosphorylate RPG1 in vivo and are susceptible to stem rust, demonstrating that phosphorylation is a prerequisite for disease resistance. Protein kinase inhibitors prevent RPG1 phosphorylation and result in susceptibility to stem rust, providing further evidence for the importance of phosphorylation in disease resistance. We conclude that phosphorylation of the RPG1 protein by the kinase activity of the pK2 domain induced by the interaction with an unknown pathogen spore product is required for resistance to the avirulent stem rust races. The pseudokinase pK1 domain is required for disease resistance but not phosphorylation. The very rapid phosphorylation of RPG1 suggests that an effector is already present in or on the stem rust urediniospores when they are placed on the leaf surface. However, spores must be alive, as determined by their ability to germinate, in order to elicit RPG1 phosphorylation.

Last Modified: 9/2/2014
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