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

Authors: GUSTINE D L - 1902-05-00; SHERWOOD R T - 1902-05-00; MOYER B G - 1902-05-00

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Evidence for a new class of peptide elicitor of the hypersensitive reaction from the tomato pathogen Pseudomonas corrugata. Although Pseudomonas corrugata is an economically important phytopathogen of tomato and pepper, strains have been used in biocontrol studies which reduce crop losses due t disease. This bacterium also induces defense responses in nonhost plants, collectively called the hypersensitive reaction (HR), that minimizes disea development. The authors discovered two small, fluorescent peptide product called elicitors, produced by cultures of P. corrugata. Each was shown to induce the HR in a nonhost plant. Equally important was the finding that each one did not cause disease in a host plant (tomato). These nonphytotox compounds, HR1 and HR2, are less than 3,500 daltons in size (most peptide, proteins, are much larger). Because P. corrugata is pathogenic on economically important crops, its direct use in biological control is not advisable. Since HR1 and HR2 are easy to produce and isolate, and since t are safe, these elicitors represent a new class of potentially useful biocontrol agents.

Technical Abstract: The hypersensitive reaction (HR) is comprised of localized nonhost plant defense responses (seen as development of a water-soaked lesion, rapid cell death and formation of dry tissue) and occurs within 24 hours. Plant defense responses and the subsequent development of HR are induced by elicitors. While Pseudomonas corrugata is a phytopathogen, strains have been used in biocontrol studies. It also elicits HR following infiltratio of its cells into tobacco leaf panels. Three elicitor-active fractions were isolated from culture fluids of P. corrugata. Lyophilized, filtered culture fluids extracted with methanol-ethyl acetate (80:20; v,v) produced a water soluble crude extract (CE). The aqueous CE fraction partitioned with ethyl acetate produced a water soluble aqueous (AQ) fraction and a purified elicitor (HR2) fraction (from three cycles of partitioning between ethyl acetate and water). P. corrugata cells and the three fractions were tested for their ability to elicit HR in tobacco leaves, tomato pith necrosis, K+/H+ exchange in tobacco tissue culture and phytoalexin (medicarpin) biosynthesis in white clover tissue culture. Only live P. corrugata cells elicited pith necrosis; both bacteria and the fractions elicited phytoalexin biosynthesis and HR; bacteria and HR2 elicited K+/H+ exchange. HR2 did not cause a spreading lesion in tobacco and was therefore not a toxin. A second elicitor, HR1, was isolated which elicited HR and phytoalexin biosynthesis. HR1 and HR2, 95 % pure by HPLC analysis, contained a fluorescent chromophore, and a peptide. They contained glutamic acid, tyrosine, aspartic acid, glycine, alanine and/or arginine and isoleucine and/or leucine (molar ratio 10:3:1:1:1:1). These elicitors may have potential use as biocontrol agents.