A plant defense signaling peptide and applications thereof for inducing systemic immune responses in a plant. In some embodiments, methods for inducing systemic immune responses in a plant comprises applying to the plant a plant defense signaling polypeptide comprising a motif of SEQ ID NO: 1 or SEQ ID NO: 28, or a composition comprising the polypeptide, wherein the polypeptide has up to 100 amino acids in length.