title: Systemin: a polypeptide signal for plant defensive genes.
abstract: Damage to leaves of several plant species by herbivores or by other mechanical wounding induces defense gene activation throughout the plants within hours. An 18-amino acid polypeptide, called systemin, has been isolated from tomato leaves that is a powerful inducer of over 15 defensive genes when supplied to the tomato plants at levels of fmol/plant. Systemin is readily transported from wound sites and is considered to be the primary systemic signal. The polypeptide is processed from a 200-amino acid precursor called prosystemin, analogous to polypeptide hormones in animals. However, the plant prohormone does not possess typical dibasic cleavage sites, nor does it contain a signal sequence or any typical membrane-spanning regions. The signal transduction pathway that mediates systemin signaling involves linolenic acid release from membranes and subsequent conversion to jasmonic acid, a potent activator of defense gene transcription. The pathway exhibits analogies to arachidonic acid/prostaglandin signaling in animals that leads to inflammatory and acute phase responses.
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman 99164-6340, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Ryan
authors.forename: G
authors.initials: G
authors.lastname: Pearce
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018506:Gene Expression Regulation, Plant; D018551:Solanum lycopersicum / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D010455:Peptides / Q000502:physiology; D018521:Plant Physiological Phenomena; D010940:Plant Proteins / Q000235:genetics / Q000502:physiology*; D010944:Plants / Q000235:genetics*; D015398:Signal Transduction; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: D010455:Peptides; D010940:Plant Proteins; C073705:prosystemin protein, Lycopersicon esculentum; C073704:systemin