PSEUDOMONAS-SYRINGAE PV SYRINGAE HARPIN (PSS) - A PROTEIN THAT IS SECRETED VIA THE HRP PATHWAY AND ELICITS THE HYPERSENSITIVE RESPONSE IN PLANTS

The ability of P. syringae to elicit the hypersensitive response in nonhost plants or pathogenesis in hosts is controlled by hrp genes. The P. syringae pv. syringae 61 hrpZ gene encodes harpin(Pss), a 34.7 kd extracellular protein that elicits hypersensitive necrosis in tobacco and other plants. Harpin(Pss) is heat stable, glycine rich, dissimilar in amino acid sequence to any known protein, produced only in apoplastic fluid-mimicking minimal media, and secreted in a HrpH-dependent manner. The carboxy-terminal 148 amino acid portion of harpin(Pss) contains two directly repeated sequences of GGGLGTP and QTGT and is sufficient and necessary for elicitor activity. The necrosis elicited by harpin(Pss) is an active response of the plant, which can be inhibited by alpha-amanitin, cycloheximide, lanthanum chloride, or sodium vanadate.