EVIDENCE FOR A NEW CLASS OF PEPTIDE ELICITOR OF THE HYPERSENSITIVE REACTION FROM THE TOMATO PATHOGEN PSEUDOMONAS-CORRUGATA

Three elicitor-active fractions were isolated from culture fluids of t he rough isolate of Pseudomonas corrugata, a tomato pathogen that elic its the hypersensitive reaction (HR) in tobacco. Lyophilized, filtered culture fluids were extracted with methanol-ethyl acetate (80:20, vol /vol) to produce a water-soluble crude extract (CE). CE was partitione d with ethyl acetate to produce water-soluble aqueous (AQ) and organic (EA) fractions containing purified elicitor. P. corrugata and the thr ee fractions were tested for their ability to elicit HR in tobacco lea ves, pith necrosis in tomato, and K+/H+ exchange in tobacco tissue cul ture. Only P. corruga'a elicited pith necrosis in tomato; both bacteri a and the fractions elicited HR in tobacco leaves; and bacteria and EA elicited K+/H+ exchange in tobacco cells. The primary component in EA , HR2, did not cause a spreading lesion in tobacco and was therefore n ot a toxin. HR2 was found to be 95% pure by analytical high-performanc e liquid chromatography, to contain a fluorescent chromophore, and to be a peptide. HR2 contains glutamic acid, tyrosine, aspartic acid, gly cine, alanine and/or arginine, isoleucine and/or leucine, and methioni ne and/or valine (approximate molar ratio 10:3:1:1:1:1:1). Since P. co rrugata is a useful biocontrol agent, these elicitors may have potenti al use in biocontrol.