Systemin: a polypeptide signal for plant defensive genes

Area of Science:

• Plant Biology
• Molecular Biology
• Biochemistry

Background:

• Mechanical wounding or herbivory in plants rapidly induces defense gene activation.
• Systemin, an 18-amino acid polypeptide, is a potent inducer of plant defense genes.
• Systemin is transported from wound sites, acting as a primary systemic signal.

Purpose of the Study:

• To isolate and characterize systemin, a key signaling molecule in plant defense.
• To elucidate the mechanism of systemin transport and its role in systemic signaling.
• To understand the signal transduction pathway mediating systemin-induced defense responses.

Main Methods:

• Isolation and purification of systemin from tomato leaves.
• Application of systemin to tomato plants to observe defense gene activation.
• Analysis of the prosystemin precursor structure.
• Investigation of the signal transduction pathway involving linolenic acid and jasmonic acid.

Main Results:

• Systemin was identified as an 18-amino acid polypeptide that induces over 15 defense genes at fmol/plant levels.
• Systemin is processed from a 200-amino acid prosystemin precursor, lacking typical animal hormone processing sites.
• The signaling pathway involves linolenic acid release and conversion to jasmonic acid, activating defense gene transcription.

Conclusions:

• Systemin is a critical endogenous signal for initiating plant defense responses.
• The systemin signaling pathway shares analogies with animal inflammatory pathways.
• Understanding systemin signaling provides insights into plant immunity and inter-kingdom signaling parallels.