Serine Protease Inhibitors Specifically Defend Solanum nigrum against Generalist Herbivores but Do Not Influence Plant Growth and Development  

Abstract

Solanaceaeous taxa produce diverse peptide serine proteinase inhibitors (SPIs), known antidigestive defenses that might also control endogenous plant proteases. If and how a plant coordinates and combines its different SPIs for the defense against herbivores and if these SPIs simultaneously serve developmental functions is unknown. We examine Solanum nigrum's SPI profile, comprising four different active inhibitors, of which the most abundant proved to be novel, to understand their functional specialization in an ecological context. Transcript and activity characterization revealed tissuespecific and insect-elicited accumulation patterns. Stable and transient gene silencing of all four SPIs revealed different specificities for target proteinases: the novel SPI2c displayed high specificity for trypsin and chymotrypsin, while two other SPI2 homologs were highly active against subtilisin. In field and lab experiments, we found all four SPIs to display herbivoreand gene-specific defensive properties, with dissimilar effects on closely related species. However, we did not observe any clear developmental phenotype in SPI-silenced plants, suggesting that SPIs do not play a major role in regulating endogenous proteases under the conditions studied. In summary, specific single SPIs or their combinations defend S. nigrum against generalist herbivores, while the defense against herbivores specialized on SPI-rich diets requires other unknown defense mechanisms.

NaStEP: A Proteinase Inhibitor Essential to Self-Incompatibility and a Positive Regulator of HT-B Stability inNicotiana alataPollen Tubes

“…However, the putative subtilisin-like component has yet to be identified, and a control mechanism for the NaStEP action remains unknown, since this protein is also present during SI pollination events, where rejection does take place. Besides their possible involvement in SI, plant proteases and protease inhibitors have been increasingly associated with several developmental processes such as plant-pathogen-insect interactions (Li et al, 2008;Hartl et al, 2010) and more recently in program cell death (Chichkova et al, 2010), which makes it a very intense field of study.…”

Mechanisms of plant defense against insect herbivores

“…14 The SPIs from Solanum nigrum L. have been found to adversely affect a number of insect pests. 77 Progress in genome sequencing has resulted in identification of a large number of proteinase inhibitors and other defense components induced in plants on account of herbivore damage. Although most of the KPIs in plants are upregulated in response to insect herbivory, their degree of induction varies as per the insect plant interaction.…”

NaJAZh Regulates a Subset of Defense Responses against Herbivores and Spontaneous Leaf Necrosis inNicotiana attenuataPlants

“…plants produce nicotinic alkaloids to ward off attack from feeding herbivores (Baldwin et al, 1997;Wink and Roberts, 1998;Shoji et al, 2000;Steppuhn et al, 2004). In addition, most plants produce protease inhibitors in response to herbivory, which inhibit proteolysis and negatively affect the digestibility of ingested plant material in insect guts (Jongsma et al, 1994(Jongsma et al, , 1995Koiwa et al, 1997;Zavala et al, 2004a;Habib and Fazili, 2007;Hartl et al, 2010). Green leaf volatiles (GLVs) and volatile organic compounds (VOCs) constitute another important plant defense mechanism to attract predators of herbivores; this strategy is also known as indirect plant defense (Halitschke et al, 2000;Kessler and Baldwin, 2001;Baldwin et al, 2002;Allmann and Baldwin, 2010).…”