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Systemin--a polypeptide defense signal in plants
1Institute of Biological Chemistry, Washington State University, Pullman 99164-6340, USA.
Summary
Systemin, an 18-amino-acid polypeptide, acts as a wound hormone in tomato plants, activating defense genes. It is derived from prosystemin and is crucial for systemic signaling in response to herbivore attacks.
Area of Science:
- Plant molecular biology
- Plant defense mechanisms
- Hormonal signaling in plants
Background:
- Insect and pathogen attacks trigger rapid plant defense responses.
- Systemic signaling coordinates defense gene activation throughout the plant.
- The identity of signaling molecules in plant defense was previously unknown.
Purpose of the Study:
- To identify signaling molecules involved in localized and systemic plant defense.
- To elucidate the role of systemin in plant wound response.
- To investigate the mechanism of systemin perception and signaling.
Main Methods:
- Identification of systemin through biochemical assays.
- Autoradiography to track systemin mobility.
- Antisense technology to assess systemin's essential role.
- Characterization of systemin-binding proteins in plant plasma membranes.
Main Results:
- Systemin, an 18-amino-acid polypeptide, was identified as a key signaling molecule.
- Systemin activates defense genes at very low concentrations (fmols/plant).
- Systemin is derived from prosystemin and is phloem-mobile.
- A systemin-binding protein with protease activity, not a receptor, was identified.
- Systemin is essential for wound-inducible, systemic signal transduction.
Conclusions:
- Systemin functions as a wound hormone in tomato plants.
- Polypeptide hormones like systemin may play broad roles in plant stress responses.
- Systemin and prosystemin serve as prototypes for plant polypeptide hormones in environmental signaling and growth regulation.