Proteome of monoclonal antibody-purified haustoria from Puccinia triticina Race-1.

Puccinia triticina causes leaf rust, a disease that causes annual yield losses in wheat. It is an obligate parasite that invades the host leaf and forms intracellular structures called haustoria, which obtain nutrients and suppress host immunity using secreted proteins called effectors. Since effector proteins act at the frontier between plant and pathogen and help determine the outcome of the interaction, it is critical to understand their functions. Here, we used a direct proteomics approach to identify effector candidates from P. triticina Race 1 haustoria isolated with a specific monoclonal antibody. Haustoria were >95% pure and free of host contaminants. Using high resolution MS we have identified 1192 haustoria proteins. These were quantified using normalized spectral counts and spanned a dynamic range of three orders of magnitude, with unknown proteins and metabolic enzymes as the most highly represented. The dataset contained 140 candidate effector proteins, based on the presence of a signal peptide and the absence of a known function for the protein. Some of these candidates were significantly enriched with cysteine, with up to 13 residues per protein and up to 6.8% cysteine in composition.