https://pubs.rsc.org/en/content/articlepdf/2019/NP/C8NP00092A

Marine natural products.

Elicitor signal transduction leading to production of plant secondary metabolites.

Summary: A major innate defense system in invertebrates is the melanization of pathogens and damaged tissues. This important process is controlled by the enzyme phenoloxidase (PO) that in turn is regulated in a highly elaborate manner for avoiding unnecessary production of highly toxic and reactive compounds. Recent progress, especially in arthropods, in the elucidation of mechanisms controlling the activation of zymogenic proPO into active PO by a cascade of serine proteinases and other factors is reviewed. The proPO-activating system (proPO system) is triggered by the presence of minute amounts of compounds of microbial origins, such as β-1,3-glucans, lipopolysaccharides, and peptidoglycans, which ensures that the system will become active in the presence of potential pathogens. The presence of specific proteinase inhibitors prevents superfluous activation. Concomitant with proPO activation, many other immune reactions will be produced, such as the generation of factors with anti-microbial, cytotoxic, opsonic, or encapsulation-promoting activities.

The prophenoloxidase-activating system in invertebrates.

Reactive oxygen species are believed to perform multiple roles during plant defense responses to microbial attack, acting in the initial defense and possibly as cellular signaling molecules. In animals, nitric oxide (NO) is an important redox-active signaling molecule. Here we show that infection of resistant, but not susceptible, tobacco with tobacco mosaic virus resulted in enhanced NO synthase (NOS) activity. Furthermore, administration of NO donors or recombinant mammalian NOS to tobacco plants or tobacco suspension cells triggered expression of the defense-related genes encoding pathogenesis-related 1 protein and phenylalanine ammonia lyase (PAL). These genes were also induced by cyclic GMP (cGMP) and cyclic ADP-ribose, two molecules that can serve as second messengers for NO signaling in mammals. Consistent with cGMP acting as a second messenger in tobacco, NO treatment induced dramatic and transient increases in endogenous cGMP levels. Furthermore, NO-induced activation of PAL was blocked by 6-anilino-5,8-quinolinedione and 1H-(1,2,4)-oxadiazole[4,3-a]quinoxalin-1-one, two inhibitors of guanylate cyclase. Although 6-anilino-5,8-quinolinedione fully blocked PAL activation, inhibition by 1H-(1,2,4)-oxadiazole[4,3-a]quinoxalin-1-one was not entirely complete, suggesting the existence of cGMP-independent, as well as cGMP-dependent, NO signaling. We conclude that several critical players of animal NO signaling are also operative in plants.

https://www.pnas.org/content/pnas/95/17/10328.full.pdf

Defense gene induction in tobacco by nitric oxide, cyclic GMP, and cyclic ADP-ribose

Microbial α-amylases: a biotechnological perspective

The antibacterial activity against MRSA strains and other bacteria of a <500Da fraction from maggot excretions/secretions of Lucilia sericata (Diptera: Calliphoridae).

Cyclic AMP and higher plants

The properties and purification of a Blaberus craniifer plasma protein which enhances the activation of haemocyte prophenoloxidase by a β 1,3-glucan

Fingerprint profile of Ginkgo biloba nutritional supplements by LC/ESI-MS/MS.

For three decades, hypotheses relating to the occurrence and function of cyclic nucleotides in higher plants have been highly controversial. Although cyclic nucleotides had been shown to have key regulatory roles in animals and bacteria, investigations with higher plants in the 1970s and early 1980s were criticized on the basis of (i) a lack of specificity of effects apparently elicited by cyclic nucleotides, (ii) the equivocal identification of putative endogenous cyclic nucleotides and (iii) ambiguity in the identification of enzymes connected with cyclic nucleotide. More recent evidence based on more rigorous identification procedures has demonstrated conclusively the presence of cyclic nucleotides, nucleotidyl cyclases and cyclic nucleotide phosphodiesterases in higher plants, and has identified plant processes subject to regulation by cyclic nucleotides. Here we review the history of the debate, the recent evidence establishing the presence of these compounds and their role; future research objectives are discussed.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-8137.1999.00478.x

Russell P. Newton

Papers

The antibacterial activity against MRSA strains and other bacteria of a <500Da fraction from maggot excretions/secretions of Lucilia sericata (Diptera: Calliphoridae).

Cyclic AMP and higher plants

The properties and purification of a Blaberus craniifer plasma protein which enhances the activation of haemocyte prophenoloxidase by a β 1,3-glucan

Fingerprint profile of Ginkgo biloba nutritional supplements by LC/ESI-MS/MS.

Tansley review No. 106, Cyclic nucleotides in higher plants : The enduring paradox