Potential cysteine protease. Avirulence protein, which may be essential during infection of plant cells from Pea and some Arabidopsis thaliana cultivars. May act by affecting the plant defense system. In plants lacking appropriate resistance (R) gene, it probably impairs the plant defense system and leads to the bacteria multiplication. In contrast, in plants containing the appropriate R protein, it is unable to induce disease symptoms, explaining its avirulence name. Belongs to the peptidase C58 family.