Systemin--a polypeptide defense signal in plants.
Insect and pathogen attacks activate plant defense genes within minutes in nearby cells, and within hours in leaves far distant from the sites of the predator attacks. A search for signal molecules involved in both the localized and distal signalling has resulted in the identification of an 18-amino-acid polypeptide, called systemin, that activates defense genes in leaves of tomato plants when supplied at levels as low as fmols/plant. Several lines of evidence support a role for systemin as a wound hormone. As with animal polypeptide hormones, systemin is derived from a larger precursor protein, called prosystemin, by limited proteolysis. Systemin has been shown by autoradiography to be phloemmobile and, by antisense technology, to be an essential component of the wound-inducible, systemic signal transduction system leading to the transcriptional activation of the defensive genes. A search for the receptor of systemin has led to the identification in plant plasma membranes of a systemin-binding protein. However, this protein has properties not of a receptor, but of a furin-like proteinase that cleaves systemin into smaller polypeptides. Systemin and its precursor prosystemin provide prototypes for the emerging possibilities that polypeptide hormones may have broad roles in signalling environmental stress responses, and in regulating plant growth and development as well.
Schaller
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Institute of Biological Chemistry, Washington State University, Pullman 99164-6340, USA.
Ryan
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CA
D000040:Abscisic Acid / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D002473:Cell Wall / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D006603:Hexuronic Acids / Q000378:metabolism; D007313:Insecta / Q000502:physiology; D008565:Membrane Proteins / Q000032:analysis; D008969:Molecular Sequence Data; D010455:Peptides / Q000502:physiology*; D010935:Plant Diseases; D018521:Plant Physiological Phenomena; D010940:Plant Proteins / Q000032:analysis / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D015398:Signal Transduction
D006603:Hexuronic Acids; D008565:Membrane Proteins; D010455:Peptides; D010940:Plant Proteins; C098316:systemin-binding protein, Lycopersicon esculentum; C073705:prosystemin protein, Lycopersicon esculentum; C073704:systemin; C007819:galacturonic acid; D000040:Abscisic Acid