Elicitor signal transduction leading to production of plant secondary metabolites.

Harnessing the toxic properties of reactive oxygen species (ROS) to fight off invading pathogens can be considered a major evolutionary success story. All aerobic organisms have evolved the ability to regulate the levels of these toxic intermediates, whereas some have evolved elaborate signalling pathways to dramatically increase the levels of ROS and use them as weapons in mounting a defence response, a process commonly referred to as the oxidative burst. The balance between steady state levels of ROS and the exponential increase in these levels during the oxidative burst has begun to shed light on complex signalling networks mediated by these molecules. Here, we discuss the different sources of ROS that are present in plant cells and review their role in the oxidative burst. We further describe two well-studied ROS generating systems, the NADPH oxidase and apoplastic peroxidase proteins, and their role as the primary producers of ROS during pathogen invasion. We then discuss what is known about the metabolic and proteomic fluxes that occur in plant cells during the oxidative burst and after pathogen recognition, and try to highlight underlying biochemical processes that may provide more insight on the complex regulation of ROS in plants.

Reactive oxygen species and their role in plant defence and cell wall metabolism

Aziz, A., Trotel-Aziz, P., Dhuicq, L., Jeandet, P., Couderchet, M., and Vernet, G. 2006. Chitosan oligomers and copper sulfate induce grapevine defense reactions and resistance to gray mold and downy mildew. Phytopathology 96:1188-1194. Chitosan (CHN), a deacetylated derivative of chitin, was shown to be efficient in promoting plant defense reactions. CHN oligomers of different molecular weight (MW) and degree of acetylation (DA) triggered an accumulation of phytoalexins, trans- and cis-resveratrol and their derivatives e-viniferin and piceid, in grapevine leaves. Highest phytoalexin production was achieved within 48 h of incubation with CHN at 200 µg/ml with an MW of 1,500 and a DA of 20% (CHN1.5/20), while oligomers with greater MW were less efficient, indicating that a specific MW threshold could be required for phytoalexin response. Treatment of grapevine leaves by highly active CHN1.5/20 also led to marked induction of chitinase and β-1,3-glucanase activities. CHN1.5/20 applied together with copper sulfate (CuSO4) strongly induced phytoalexin accumulation. CuSO4 alone, especially at low concentrations also elicited a substantial production of phytoalexins in grapevine leaves. Evidence is also provided that CHN1.5/20 significantly reduced the infection of grapevine leaves by Botrytis cinerea and Plasmopara viticola, and in combination with CuSO4 conferred protection against both pathogens.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-96-1188

Chitosan oligomers and copper sulfate induce grapevine defense reactions and resistance to gray mold and downy mildew.

Plants are a nearly unlimited source of phytochemicals. The plants produce various secondary metabolites, which are useful in its interaction with the environment, various stress factors and development of resistance against pathogen attack. A wide array of external stimuli are capable of triggering changes in the plant cell which leads to a cascade of reactions, ultimately resulting in the formation and accumulation of secondary metabolites which helps the plant to overcome the stress factors. The biotic and abiotic elicitors can result in an enhancement of the secondary metabolite production. The stimuli are perceived by receptors, which then result in the activation of the secondary messengers. These then transmit the signals into the cell through the signal transduction pathways leading to gene expression and biochemical changes. There is interplay of the signaling molecules also which regulates the entire pathway. This review is oriented towards the factors, which influence signal transduction pathway(s) with special reference to polyamines, calcium, jasmonates, salicylates, nitric oxide and ethylene. The interplay of these components to elicit a defense response is discussed. Molecular aspects of disease resistance and regulation of plant secondary metabolism has also been presented.

Involvement and interaction of various signaling compounds on the plant metabolic events during defense response, resistance to stress factors, formation of secondary metabolites and their molecular aspects.

Microbial plant pathogens have evolved a variety of strategies to enter plant hosts and cause disease. In particular, biotrophic pathogens, which parasitize living plant tissue, establish sophisticated interactions in which they modulate the plant's metabolism to their own good. The prime decision, whether or not a pathogen can accommodate itself in its host tissue, is made during the initial phase of infection. At this stage, the plant immune system recognizes conserved molecular patterns of the invading microbe, which initiate a set of basal immune responses. Induced plant defense proteins, toxic compounds and antimicrobial proteins encounter a broad arsenal of pathogen-derived virulence factors that aim to disarm host immunity. Crucial regulatory processes and protein-protein interactions take place in the apoplast, that is, intercellular spaces, plant cell walls and defined host-pathogen interfaces which are formed between the plant cytoplasm and the specialized infection structures of many biotrophic pathogens. This article aims to provide an insight into the most important principles and components of apoplastic plant immunity and its modulation by filamentous microbial pathogens.

Apoplastic immunity and its suppression by filamentous plant pathogens.

Summary
• The effects are reported here of an elicitor prepared from liquid cultures of an isolate of Verticillium albo-atrum, which is nonpathogenic to Medicago sativa, on accumulation of H2O2, medicarpin, deposition of phenolic polymer and phenylalanine ammonia-lyase (PAL) activity in cultured cells of Medicago sativa L. cv. Kabul (lucerne).
• PAL activity and phytoalexins were assayed spectrophotometically and by HPLC, respectively. The scopoletin fluorescence-quenching and thioglycolic acid methods were used to measure H2O2 and phenolic polymer deposition, respectively.
• Studies with inhibitors suggested that an NAD(P)H oxidase and a peroxidase were involved in the elicitor stimulated accumulation of H2O2 and that an increase in cytosolic Ca2+, but not H2O2, was part of a signalling pathway leading to the induction of defence responses.
• Both the influx of Ca2+ and release of Ca2+ from intracellular stores forms part of the signalling pathway leading from perception of elicitor to induction of defence responses. Although H2O2 is not part of the pathway, evidence is presented that O2− is part of the signal transduction chain.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-8137.2001.00062.x

Elicitor induced defence responses in medicago sativa

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Elicitor induced defence responses in medicago sativa