A Harpin Binding Site in Tobacco Plasma Membranes Mediates Activation of the Pathogenesis-Related Gene HIN1 Independent of Extracellular Calcium but Dependent on Mitogen-Activated Protein Kinase Activity

• Published in: The Plant cell Vol. 13; no. 5; pp. 1079 - 1093
• Main Authors: Lee, Justin, Klessig, Daniel F., Nürnberger, Thorsten
• Format: Journal Article
• Language: English
• Published: England American Society of Plant Physiologists 01-05-2001; American Society of Plant Biologists
• Subjects: Bacterial Outer Membrane Proteins - metabolism; Binding Sites; Binding, Competitive; Cell Membrane - metabolism; Cell membranes; Cell walls; Fungal Proteins - pharmacology; Gene Expression Regulation; Gene Expression Regulation, Plant; Genes; harpin; HIN1 gene; Ligands; mitogen-activated protein kinase; Mitogen-Activated Protein Kinases - metabolism; Nicotiana - genetics; Nicotiana - metabolism; Peptide Fragments - metabolism; Plant cells; Plant Diseases - genetics; Plant Growth Regulators - pharmacology; Plant Proteins - biosynthesis; Plant Proteins - genetics; Plants; Plants, Toxic; Proteins; Psph gene; Reverse transcriptase polymerase chain reaction; RNA; Salicylic Acid - pharmacology
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.13.5.1079

Harpin from the bean halo-blight pathogen Pseudomonas syringae pv phaseolicola $(\text{harpin}_{{\rm Psph}})$ elicits the hypersensitive response and the accumulation of pathogenesis-related gene transcripts in the nonhost plant tobacco. Here, we report the characterization of a nonproteinaceous binding site for $\text{harpin}_{{\rm Psph}}$ in tobacco plasma membranes, which is assumed to mediate the activation of plant defense responses in a receptor-like manner. Binding of ^{125}{\rm I}\text{-harpin}_{{\rm Psph}}$ to tobacco microsomal membranes (dissociation constant = 425 nM) and protoplasts (dissociation constant = 380 nM) was specific, reversible, and saturable. A close correlation was found between the abilities of $\text{harpin}_{{\rm Psph}}$ fragments to elicit the transcript accumulation of the pathogenesis-related tobacco gene HIN1 and to compete for binding of ^{125}{\rm I}\text{-harpin}_{{\rm Psph}}$ to its binding site. Another elicitor of the hypersensitive response and HIN1 induction in tobacco, the Phytophthora megasperma-derived β-elicitin β-megaspermin, failed to bind to the putative $\text{harpin}_{{\rm Psph}}$ receptor. In contrast to activation by β-megaspermin, $\text{harpin}_{{\rm Psph}}\text{-induced}$ activation of the 48-kD salicylic acid-responsive mitogen-activated protein kinase (MAPK) and HIN1 transcript accumulation were independent of extracellular calcium. Moreover, use of the MAPK kinase inhibitor U0126 revealed that MAPK activity was essential for pathogenesis-related gene expression in $\text{harpin}_{{\rm Psph}}\text{-treated}$ tobacco cells. Thus, a receptor-mediated MAPK-dependent signaling pathway may mediate the activation of plant defense responses induced by $\text{harpin}_{{\rm Psph}}$.