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A gene that encodes systemin, a mobile 18-amino acid polypeptide inducer of proteinase inhibitor synthesis in tomato and potato leaves, has been isolated from tomato, Lycopersicon esculentum. Induction of proteinase inhibitors in plants is a response to insect or pathogen attacks. The gene has 10 introns and 11 exons, ten of which are organized as five homologous pairs with an unrelated sequence in the eleventh, encoding systemin. Systemin is proteolytically processed from a 200-amino acid precursor protein, prosystemin. Prosystemin messenger RNA was found in all organs of the plant except the roots and was systemically wound-inducible in leaves. Tomato plants transformed with an antisense prosystemin complementary DNA exhibited greatly suppressed systemic wound induction of proteinase Inhibitor I and II synthesis in leaves.
McGurl et al. (Fri,) studied this question.