Purification and characterization of two novel hypersensitive response-inducing specific elicitors produced by the cowpea rust fungus

Two novel elicitor peptides that are produced by the race 1 of the cowpea rust fungus Uromyces vignae and that specifically induce a hypersensitive response (a putative form of programmed cell death) in a resistant cultivar of cowpea (Vigna unguiculata L. Walp) have been purified to homogeneity. Purification steps included gel filtration, anion-exchange chromatography, continuous elution electrophoresis, and reversed-phase C-18 high performance liquid chromatography. The relative molecular masses of the peptide elicitors as deduced from Tricine sodium dodecyl sulfate-polyacrylamide gel electrophoresis were 5600 Da (major) and 5800 Da (minor), respectively. Peptide 1 (major) and the minor copurifying peptide (peptide 2) resolved at the final C-18 high performance liquid chromatography step. The NH2 terminus of peptide 1 was deblocked with anhydrous trifluoroacetic acid prior to sequencing. However, the NH2 terminus of peptide 2 was free. The acidic and hydrophobic peptides show some homology between themselves but do not show any significant similarity with known proteins. The two specific elicitors may be products of two avirulence genes corresponding to the two genes for resistance in the resistant cultivar.