Systemin

Systemin is a plant peptide hormone involved in systemic wound response, primarily in the Solanaceae family (which includes tomatoes, potatoes, and eggplant). It is an 18-amino acid peptide derived from a larger precursor protein called prosystemin.

Mechanism of Action:

Upon wounding, such as herbivore attack, prosystemin is released and processed into the active systemin peptide. Systemin then binds to a plasma membrane receptor, Systemin Receptor 1 (SR1), also known as a leucine-rich repeat receptor kinase (LRR-RK). This binding initiates a signaling cascade, leading to the activation of jasmonic acid (JA) biosynthesis. Jasmonic acid is a key phytohormone involved in plant defense.

Role in Plant Defense:

The increased JA levels trigger the expression of genes encoding defense proteins, such as proteinase inhibitors (PIs). These proteinase inhibitors interfere with the digestive systems of herbivores, making the plant less palatable and hindering their ability to extract nutrients. Systemin, therefore, acts as a systemic signal, alerting distant tissues to the presence of a wound and inducing a whole-plant defense response.

Systemic Signaling:

The term "systemic" refers to the ability of systemin to travel throughout the plant via the phloem, enabling it to initiate defensive responses in tissues far removed from the initial site of injury. This long-distance signaling is crucial for coordinated plant defense.

Discovery and Significance:

Systemin was one of the first plant peptide hormones to be identified and characterized. Its discovery significantly contributed to our understanding of plant signaling pathways and systemic wound responses. Research continues to explore the complexities of systemin signaling and its potential applications in agriculture, particularly in enhancing plant resistance to pests.