PROSYSTEMIN FROM POTATO, BLACK NIGHTSHADE, AND BELL PEPPER - PRIMARY STRUCTURE AND BIOLOGICAL-ACTIVITY OF PREDICTED SYSTEMIN POLYPEPTIDES

Prosystemin is the precursor protein of the 18 amino acid wound signal systemin which activates systemic defense in tomato leaves against in sect herbivores (McGurl B, Pearce G, Orozco-Cardenas M, Ryan CA, Scien ce 255 (1993) 1570-1573) Here Wp report thp isolation nf cDNA sequence s encoding prosystemin from potato (Solanum tuberosum) black nightshad e, (S. nigrum), and bell pepper (Capsicum annuum) all members of the S olanaceae family, using reverse-transcription polymerase chain reactio n (RT-PCR). Pairwise comparisons of the predicted prosystemin proteins from the three species with tomato prosystemin and among each other i ndicated sequence identities ranging from 73% to 88%. The deduced syst emin polypeptides were synthesized and tested for their capacities to induce the synthesis of the defensive proteinase inhibitors in tomato leaves. Potato and pepper systemins were approximately as active as to mato systemin, whereas nightshade systemin was ten-fold less active. T he accumulation of proteinase inhibitor mRNA transcripts could be indu ced in each of these plants by treatment with the homologous systemin. As in the tomato, in potato, black nightshade, and bell pepper plants , prosystemin homologs appear to function as precursors of systemic wo und signals.