Systemin is a plant peptide hormone involved in the wound response in the Solanaceae plant family, first plant peptide hormone found in tomato leaves. Systemin activates a lipid-based signal transduction pathway involved in defense gene transcription. The peptide corresponds to the mature sequence (aa 179-196) of systemin precursor.H-Ala-Val-Gln-Ser-Lys-Pro-Pro-Ser-Lys-Arg-Asp-Pro-Pro-Lys-Met-Gln-Thr-Asp-OH or H-AVQSKPPSKRDPPKMQTD-OH