Systemin signal

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... 

In tomato and potato plants, two families of Pis have been identified that show wound-inducible expression. Within 48 h after wounding of leaves of these plants, up to 2% of leaf protein content is made up of protease inhibitors. Potato type I (Potl) inhibitors are not only expressed in wounded leaves but also in tissue of leaves away from the site of attack. ° This finding prompted the search for a hormone or inducing factor that carries the signal for enhanced inhibitor expression through the plant system. Systemin, an 18-residue peptide hormone, has since been reported to induce more than 15 genes of defense nature in tomatoes. ... 

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].

Whereas systemin is a peptide signal involved in the regulation of plant defense responses [14,67], phytosulfokines appear to be the first true plant peptide growth regulators. They clearly display mitogenic... 

RYAN, C.A., PEARCE, G., Systemins A functionally defined family of peptide signal that regulate defensive genes in Solanaceae species, Proc. Natl. Acad. Sci. USA, 2003, 100, 14577-14580. 

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