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The AvrM Effector from Flax Rust Has a Structured C-Terminal Domain and Interacts Directly with the M Resistance Protein

¹Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley 94720-3102, U.S.A.; ²Commonwealth Scientific and Industrial Research Organisation, Division of Plant Industry, GPO Box 1600, Canberra ACT 2601, Australia; ³School of Chemistry and Molecular Biosciences and Institute for Molecular Bioscience, University of Queensland, Brisbane QLD 4072, Australia

In plant immunity, recognition of pathogen effectors by plant resistance proteins leads to the activation of plant defenses and a localized cell death response. The AvrM effector from flax rust is a small secreted protein that is recognized by the M resistance protein in flax. Here, we investigate the mechanism of M--AvrM recognition and show that these two proteins directly interact in a yeast two-hybrid assay, and that this interaction correlates with the recognition specificity observed for each of the different AvrM variants. We further characterize this interaction by demonstrating that the C-terminal domain of AvrM is required for M-dependent cell death, and show that this domain also interacts with the M protein in yeast. We investigate the role of C-terminal differences among the different AvrM proteins for their involvement in this interaction and establish that M recognition is hindered by an additional 34 amino acids present at the C terminus of several AvrM variants. Structural characterization of recombinant AvrM-A protein revealed a globular C-terminal domain that dimerizes.