Prosystemin

Fig. (1). The wound response in tomato plants. Tomato plants respond to wounding with the transcriptional activation and accumulation of Systemic Wound Response Proteins including defense proteins, proteolysis-associated proteins, signaling-associated proteins, and proteins of yet unknown function in plants defense. The change in gene expression can be monitored on SDS-PAGE gels. In comparison to control plants (I), treatment with systemin (II), or overexpression of the prosystemin cDNA (III) leads to the accumulation of SWRPs (arrowheads) and the downregulation of other, unidentified proteins (triangles). The figure was modified after [13].

Fig. (2). The primary structure of tomato (pro)systemin. The amino acid sequence deduced from the prosystemin cDNA is shown. The systemin precursor comprises 200 amino acids. The 18 amino acids of the systemin oligopeptide (bold, underlined) are located close to the carboxy terminus.

In addition to the problem of how the systemin signal is perceived and transduced in target tissues, another complex of open questions revolves around the factors governing systemin synthesis and degradation. Systemin is synthesized as 200-amino-acid precursor protein, prosystemin (Fig. (2) [35]). In analogy to animal systems, it had been assumed that... 

Another putative hormone involved in pathogen resistance in plants is the peptide systemin [104] (Fig. If). This 18-amino acid peptide is produced from a much longer precursor, called prosystemin, upon wounding of tomato leaves, and induces proteinase inhibitors I and II in adjacent leaves. Wounding also induces the synthesis of the precursor, prosystemin. Systemin overproduction by roots induces the proteinase inhibitors constitutively in all parts of the plant, while the antisense gene for prosystemin inhibits the development of pathogen resistance [105]. The action of systemin may be via synthesis of JA, which acts as a second messenger in the induction of the proteinase inhibitors [104]. 

LI, C.Y., LIU, G.H., XU, C.C., LEE, G.I., BAUER, P., LING, H.Q., GANAL, M.W., HOWE, G.A., The tomato Suppressor of prosystemin-mediated responses2 gene encodes a fatty acid desaturase required for the biosynthesis of jasmonic acid and the production of a systemic wound signal for defense gene expression. Plant Ce//, 2003,15, 1646-1661. 

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