sistemins

Systemins are plant peptide signals that coordinate systemic defense responses to wounding and herbivory. They are produced as part of larger precursor proteins, typically referred to as prosystemin, in damaged or nearby tissues and are processed into active peptide forms that can move to distant tissues to prime defenses.

The best characterized member is the tomato systemin, an 18‑amino‑acid peptide. Systemins belong to a family that includes related peptides in other Solanaceae and, in broader terms, systemin‑like signals have been identified in various plant lineages. The prosystemin gene is often upregulated by tissue damage, enabling a rapid amplification of defense signaling throughout the plant.

Mechanistically, systemin activates the octadecanoid (jasmonic acid, JA) pathway. This leads to increased JA biosynthesis and the expression of defense genes, including proteinase inhibitors and other protective proteins. Although JA signaling is central to the response, the precise receptor for systemin and the initial perception mechanism remain areas of ongoing research. Downstream, signaling involves calcium fluxes, mitogen‑activated protein kinase cascades, and hormonal cross‑talk that modulates the strength and scope of the response. The JA pathway ultimately integrates with other hormonal signals to tailor defenses to specific attackers.

Ecologically, systemin signaling enhances plant protection against chewing herbivores and can influence neighboring plants and subsequent herbivore interactions. Its study has informed understanding of plant systemic communication and offers potential applications in crop protection through manipulation of peptide signaling pathways.