Two highly homologous MAPKs, LeMPK1 and LeMPK2, were activated in response to systemin, four different OEs, and UV-B radiation

Two highly homologous MAPKs, LeMPK1 and LeMPK2, were activated in response to systemin, four different OEs, and UV-B radiation. set of LeMPKs than the elicitors. These differences may account for UV-B-specific DKK1 responses. Plants have developed sophisticated defensive and protective responses to the various forms of stress they encounter in their environment. It has become increasingly evident that the underlying stress signaling pathways overlap and interact substantially. Although there is a remarkable specificity for stress signal perception, the signaling pathways and the resulting responses often appear to be rather unspecific. On an evolutionary scale, this may provide a basis for rapid and versatile adaptations to changing environmental challenges. For an individual plant, this may allow for an efficient response to several stressors present at the same time, a scenario plants often encounter in their environment. The systemin-mediated wound response in tomato plants is a well-investigated stress response. Systemin, an 18-amino acid wound-signaling peptide, is produced at wound sites in response to attack by herbivorous insects, and is perceived by the systemin receptor SR160, a Leu-rich repeat receptor kinase (Scheer and Ryan, 2002). Systemin is required for the systemic expression of defensive proteinase inhibitor (genes are expressed in response to oligosaccharide elicitors (OEs; Walker-Simmons and Ryan, 1984; Doares et al., 1995; Howe et al., 1996; Ramonell et al., 2002). OEs are general (nonhost-specific) elicitors derived from fungal or plant cell wall material and released in response to fungal, oomycyte, or insect attack. The elicitors are perceived by specific cell surface receptors but largely activate the same signaling components as systemin, including ion fluxes (Felix and Boller, 1995; Moyen et al., 1998; Lecourieux et al., 2002), phospholipase A2 (Narvez-Vsquez et al., 1999), NADPH oxidase (Low and Merida, 1996; Orozco-Crdenas Cysteamine HCl et al., 2001), jasmonate (Doares et al., 1995; Howe et al., 1996), and ethylene (O’Donnell et al., 1996). PIs are Cysteamine HCl Cysteamine HCl known to interfere with digestive proteases in insect guts. A dysfunctional PI defense system has been shown to severely compromise the resistance of tomato plants against herbivorous insects (Orozco-Cardenas et Cysteamine HCl al., 1993). Consistent with their synthesis in response to pathogen-derived elicitors, PIs have been shown to possess antimicrobial properties (Pautot et al., 1991; Linthorst et al., 1993; Terras et al., 1993; Giudici et al., 2000). Responses to biotic stressors often overlap with responses to abiotic stress such as UV-B radiation (280C320 nm), a portion of solar radiation that reaches the surface of the earth and is well known to cause damage to cellular macromolecules in plants (Jansen et al., 1998; Mazza et al., 1999). UV-B coordinates the regulation of sets of defense-related and other genes that are activated via different signaling pathways involving reactive oxygen species, salicylic acid, jasmonate, and ethylene (Green and Fluhr, 1995; A.-H.-Mackerness et al., 1999, 2001; Brosch et al., 2002). We had previously shown that UV-B activates components of the systemin signaling pathway and provided evidence that UV-B may activate the systemin receptor SR160 (Yalamanchili and Stratmann, 2002). It is unlikely that receptor activation by UV-B is limited to the systemin receptor; other membranebound receptors may also be activated. Receptor activation in response to UV radiation is well known in animal epidermal cells where a range of growth factor/cytokine receptors are activated by UV-B (Sachsenmaier et al., 1994; Herrlich and B?hmer, Cysteamine HCl 2000). For the epidermal growth factor receptor (EGFR), it was suggested that oxidative UV stress.