Synthetic plant defense elicitors

Abstract

To defend themselves against invading pathogens plants utilize a complex regulatory network that coordinates extensive transcriptional and metabolic reprogramming. Although many of the key players of this immunity-associated network are known, the details of its topology and dynamics are still poorly understood. As an alternative to forward and reverse genetic studies, chemical genetics-related approaches based on bioactive small molecules have gained substantial popularity in the analysis of biological pathways and networks. Use of such molecular probes can allow researchers to access biological space that was previously inaccessible to genetic analyses due to gene redundancy or lethality of mutations. Synthetic elicitors are small drug-like molecules that induce plant defense responses, but are distinct from known natural elicitors of plant immunity. While the discovery of some synthetic elicitors had already been reported in the 1970s, recent breakthroughs in combinatorial chemical synthesis now allow for inexpensive high-throughput screens for bioactive plant defense-inducing compounds. Along with powerful reverse genetics tools and resources available for model plants and crop systems, comprehensive collections of new synthetic elicitors will likely allow plant scientists to study the intricacies of plant defense signaling pathways and networks in an unparalleled fashion. As synthetic elicitors can protect crops from diseases, without the need to be directly toxic for pathogenic organisms, they may also serve as promising alternatives to conventional biocidal pesticides, which often are harmful for the environment, farmers and consumers. Here we are discussing various types of synthetic elicitors that have been used for studies on the plant immune system, their modes-of-action as well as their application in crop protection.

Salicylic acid mitigates physiological and proteomic changes induced by the SPCP1 strain of Potato virus X in tomato plants

“…As in previous work with the CP4-PVX strain [19], SA restores the photosynthetic rate in SPCP1-PVX-infected tomato plants. According to results in the present study, this recovery could be attributed to a rise in mesophyll conductance (g m ), as previously reported in other plant-virus pathosystems [8,21,56]. Conversely, although SA treatment induced an increase in R d , potentially associated to the stimulation of alternative oxidase pathways [40], this was only observed in the control plants, and does not explain the reported changes in photosynthetic rates.…”

“…Tables 2 and 3 show up or down regulation of protein expression observed in the experiment in which SA at 1.5 mM produced consistent results. Comparison of the proteomes of healthy, SA-treated (1.5 mM), and PVX-infected tomato plants at different sampling times showed that most differentially expressed proteins are involved in photosynthesis, electron transport, and plant stress responses, rather consistent with physiological changes induced by SA in our experiments and reported in other plant-virus interactions [8,45]. Only values and comparisons with significant differences are shown in Tables 2 and 3, and almost null values are excluded.…”

The Synthetic Elicitor 2-(5-Bromo-2-Hydroxy-Phenyl)-Thiazolidine-4-Carboxylic Acid Links Plant Immunity to Hormesis

“…One of them, BHTC, has not been reported as a synthetic elicitor and has a chemical structure distinct from DCA or any other plant defense inducers described so far (Schreiber and Desveaux, 2008;Knoth et al, 2009;Bektas and Eulgem, 2014). BHTC activated reporter gene expression in 1-week-old CaBP22…”

“…The disquiet over the dangers of pesticides has spawned considerable interest in alternative methods of disease control (Pimentel and Pimentel, 2008). Plant defense-inducing chemicals (plant activators and synthetic elicitors), which protect plants from diseases by activating their innate immune responses without the need of being toxic to pathogens, offer an attractive alternative for disease-control regimes that can be environmentally friendly (Bektas and Eulgem, 2014). Examples of such compounds include 2,6-dichloroisonicotinic acid (INA) and acibenzolar-S-methyl benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH; Métraux et al, 1991;Ward et al, 1991;Uknes et al, 1992).…”

“…Examples of such compounds include 2,6-dichloroisonicotinic acid (INA) and acibenzolar-S-methyl benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH; Métraux et al, 1991;Ward et al, 1991;Uknes et al, 1992). Interactions of these compounds with the plant immune system have been well characterized, and both INA and BTH are known to trigger a profile of defense-associated responses related to those triggered by SA-dependent signaling mechanisms Görlach et al, 1996;Lawton et al, 1996;Bektas and Eulgem, 2014).…”