Systemin in Solanum nigrum. The Tomato-Homologous Polypeptide Does Not Mediate Direct Defense Responses

Abstract

We extend Ryan's seminal work on the 18-amino acid polypeptide systemin in tomato's (Solanum lycopersicum) systemic wound response to the closely related solanaceous species Solanum nigrum. We compared wild-type plants to plants transformed with an inverted repeat prosystemin construct (IRSys) to silence the expression of the endogenous S. nigrum prosystemin gene. In wild-type plants elicited with wounding 1 oral secretions from Manduca sexta larvae, trypsin-proteinase inhibitors (TPIs) accumulated even though prosystemin transcripts were down-regulated. Neither reducing the endogenous systemin levels by RNAi nor complementing the plants with systemin by exogenously supplying the polypeptide through excised stems significantly increased TPI activity, indicating that systemin and TPIs are not correlated in S. nigrum. The performance of two herbivore species from two feeding guilds, M. sexta larvae and Myzus persicae nicotianae, did not differ between wild-type and IRSys plants, demonstrating that varying endogenous systemin levels do not alter the direct defenses of S. nigrum. Field experiments with wild-type and IRSys plants and the flea beetle Epitrix pubescens supported these glasshouse data. That levels of oral secretion-elicited jasmonic acid did not differ between wild-type and IRSys plants suggests that systemin is unlikely to mediate jasmonate signaling in S. nigrum as it does in tomato. We conclude that the tomato-homologous polypeptide does not mediate direct defense responses in S. nigrum.

Down-regulation of systemin after herbivory is associated with increased root allocation and competitive ability in Solanum nigrum

“…Seeds of S. nigrum inbred WT and an inbred invertedrepeat prosystemin line (IRSys plant) were germinated as previously described (Schmidt and Baldwin 2006) and transferred into either 1-l pots or 2-l pots containing a peatbased substrate (Klasmann Tonsubstrat, Geeste-Gro Hesepe, Germany) or into 1-l pots containing quartz sand (particle size 0.7-1.2 mm; Euroquarz, Germany) 21, 17 or 16 days post-sowing. The plants were grown in the glasshouse of the Max Planck Institute for Chemical Ecology (Jena, Germany) under the light, temperature, and humidity conditions previously described (Schmidt and Baldwin 2006).…”

“…The plants were grown in the glasshouse of the Max Planck Institute for Chemical Ecology (Jena, Germany) under the light, temperature, and humidity conditions previously described (Schmidt and Baldwin 2006). Every watering event supplied all plants with 0.5 g/l combination fertilizer containing phosphate, potassium, and magnesium (EuXor, Germany) and 0.5 g/l Ca(NO 3 ) 2 (MERCK, Germany).…”

“…After attack by the Xea beetle Expitrix pubescens or methyl jasmonate (MeJA) elicitation, S. nigrum systemically increases trypsin-proteinase inhibitor (TPI) activity as a direct resistance trait (Schmidt et al 2004). This response can also be induced by a treatment involving wounding and the application of Manduca sexta oral secretions (OS) to the wounds (Schmidt and Baldwin 2006). Such OS-elicitation mimics the responses elicited by herbivore attack and thus represents a useful way of inducing plants in a standardized manner.…”

“…In addition to the induction of TPIs, another response of S. nigrum to simulated herbivory by OS-elicitation is the rapid and dramatic transcriptional down-regulation of prosystemin (Schmidt and Baldwin 2006), the precursor of the peptide hormone systemin. Systemin has been intensively studied in tomato (Solanum lycopersicum L.) over the past decade and its up-regulation in wounded tomato plants has been shown to lead to TPI production (McGurl et al 1992).…”

“…However, S. nigrum does not rely on systemin to mediate direct resistance responses (Schmidt and Baldwin 2006). In OS-elicited WT plants, TPIs accumulated even though prosystemin transcripts were down-regulated.…”