Systemin – a polypeptide defense signal in plants

Abstract

Insect and pathogen attacks activate plant defense genes within minutes in nearby cells, and within hours in leaves far distant from the sites of the predator attacks. A search for signal molecules involved in both the localized and distal signalling has resulted in the identification of an 18-amino-acid polypeptide, called systemin, that activates defense genes in leaves of tomato plants when supplied at levels as low as fmols/plant. Several lines of evidence support a role for systemin as a wound hormone. As with animal polypeptide hormones, systemin is derived from a larger precursor protein, called prosystemin, by limited proteolysis. Systemin has been shown by autoradiography to be phloemmobile and, by antisense technology, to be an essential component of the wound-inducible, systemic signal transduction system leading to the transcriptional activation of the defensive genes. A search for the receptor of systemin has led to the identification in plant plasma membranes of a systemin-binding protein. However, this protein has properties not of a receptor, but of a furin-like proteinase that cleaves systemin into smaller polypeptides. Systemin and its precursor prosystemin provide prototypes for the emerging possibilities that polypeptide hormones may have broad roles in signalling environmental stress responses, and in regulating plant growth and development as well.

Systemin Potentiates the Oxidative Burst in Cultured Tomato Cells1

“…The currently acknowledged properties of systemin, in contrast, indicate that it is generated during herbivore feeding and acts to induce systemic protection against herbivores (Farmer and Ryan, 1990;Schaller and Ryan, 1995). Therefore, augmentation of the oxidative burst by pretreatment with systemin implies that a wounded tomato may have evolved strategies to prophylactically counteract opportunistic pathogens.…”

“…Systemin-mediated activation of the octadecanoid pathway culminates in the transcription of proteinase inhibitor genes that are thought to contribute to herbivore resistance (Farmer and Ryan, 1992;Mueller et al, 1993;Schaller and Ryan, 1995). Consequently, it seemed prudent to investigate whether systemin-mediated enhancement of the oxidative burst might also require de novo protein synthesis.…”

Opposite Effects on Spodoptera littoralis Larvae of High Expression Level of a Trypsin Proteinase Inhibitor in Transgenic Plants

“…They are known to be involved in several physiological processes, such as reserve control and defense against pathogens and pests ( Koiwa et al, 1997). In the latter case, PIs have been shown to be developmentally expressed in seeds and reserve organs (Birk, 1994;Koiwa et al, 1997) or induced by wounding in leaves (Schaller and Ryan, 1995). The natural protective role of PIs against phytophageous insects and the availability of PI-encoding sequences encouraged the development of pest-resistance programs based on PI expression in transgenic plants (Ryan, 1990).…”

Exploiting cucurbitaceous species as rootstocks for management of Fusarium wilt (Fusarium oxysporum) in bitter gourd

“…PPO is induced via octadecanoid defense signal pathway which is usually associated with feeding by insects or similar physical trauma. It involves jasmonic acid as an intermediate signal and culminates in the production of proteins such as PPO and proteinase inhibitors (Schaller and Ryan, 1995). The PPO activity varied significantly among rootstocks and bitter gourd scions under in intro.…”