Systemin

Orozco-Cardenas ML, Ryan CA (1999) Hydrogen peroxide is generated systemically in plant leaves by wounding and systemin via the octadecanoid pathway. Proc Natl Acad Sci USA 96 6553-6557... 

Orozco-Cardenas ML, Narvaez-Vasquez J, Ryan CA (2001) Hydrogen peroxide acts as a second messenger for the induction of defense genes in tomato plants in response to wounding, systemin, and methyl jasmonate. Plant Cell 13 179-191 Palmer CJ, Anders TL, Carpenter LJ, Ktipper FC, McFiggans G (2005) Iodine and halocarbon response of Laminaria digitata to oxidative stress and links to atmospheric new particle production. Environ Chem 2 282-290... 

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].

Sequence analysis of the defense gene-inducing principle isolated from tomato leaves revealed the amino acid sequence AVQSKPPSKRDPPK-MQTD as the primary structure of systemin (Fig. (2)). The most salient... 

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.

Systemin derivatives with Ala substitutions for any of the other proline residues, however, retained most (>10%) of the bioactivity [24]. 

Progress was made possible by use of a different source for membrane preparations. It had been shown by Felix and Boiler [26] that cell suspension cultures of a wild tomato species (Lycopersicon peruvianum) give a characteristic response to systemin. After addition of systemin an alkalinization of the culture medium was observed paralleled by an efflux of K+. Systemin also caused an increase in the activities of 1-... 

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... 

Systemin exerts its biological activity at extremely low concentrations (fmol/plant). Therefore, in analogy to animal systems, proteases have to be postulated that inactivate systemin and clear the system from residual active hormone. Experimental data indeed support the existence of such enzymes. Felix and Boiler observed that the transient nature of systemin-triggered alkalinization response in L. peruvianum cells is due to proteolytic inactivation of systemin rather than desensitization of the perception system [26]. Inactivation of systemin was, in fact, observed in... 

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... 

Orozco-Cardenas M, Ryan CA (1999) Hydrogen Peroxide is Generated Systematically in Plant Leaves by Wounding and Systemin Via the Octadecanoid Pathway. Proc Natl Acad Sci U S A 96 6553... 

Figure 38 Amino acid sequences of systemines (a-c), RALF (d), and AtPep (e). P, hydroxyprolines with glycoside chain.

---