Phytoalexins in defense against pathogens

Fungi and plants are rich sources of thousands of secondary metabolites. The genetically coded possibilities for secondary metabolite production, the stimuli of the production, and the special phytotoxins basically determine the microscopic fungi-host plant interactions and the pathogenic lifestyle of fungi. The review introduces plant secondary metabolites usually with antifungal effect as well as the importance of signaling molecules in induced systemic resistance and systemic acquired resistance processes. The review also concerns the mimicking of plant effector molecules like auxins, gibberellins and abscisic acid by fungal secondary metabolites that modulate plant growth or even can subvert the plant defense responses such as programmed cell death to gain nutrients for fungal growth and colonization. It also looks through the special secondary metabolite production and host selective toxins of some significant fungal pathogens and the plant response in form of phytoalexin production. New results coming from genome and transcriptional analyses in context of selected fungal pathogens and their hosts are also discussed.

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Secondary metabolites in fungus-plant interactions

Plant secondary metabolites carry out numerous functions in interactions between plants and a broad range of other organisms. Experimental evidence strongly supports the indispensable contribution of many constitutive and pathogen-inducible phytochemicals to plant innate immunity. Extensive studies on model plant species, particularly Arabidopsis thaliana, have brought significant advances in our understanding of the molecular mechanisms underpinning pathogen-triggered biosynthesis and activation of defensive secondary metabolites. However, despite the proven significance of secondary metabolites in plant response to pathogenic microorganisms, little is known about the precise mechanisms underlying their contribution to plant immunity. This insufficiency concerns information on the dynamics of cellular and subcellular localization of defensive phytochemicals during the encounters with microbial pathogens and precise knowledge on their mode of action. As many secondary metabolites are characterized by their in vitro antimicrobial activity, these compounds were commonly considered to function in plant defense as in planta antibiotics. Strikingly, recent experimental evidence suggests that at least some of these compounds alternatively may be involved in controlling several immune responses that are evolutionarily conserved in the plant kingdom, including callose deposition and programmed cell death.

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/nph.13325

Secondary metabolites in plant innate immunity: conserved function of divergent chemicals

Salt-tolerant plants grow in a wide variety of saline habitats, from coastal regions, salt marshes and mudflats to inland deserts, salt flats and steppes. Halophytes living in these extreme environments have to deal with frequent changes in salinity level. This can be done by developing adaptive responses including the synthesis of several bioactive molecules. Consequently, several salt marsh plants have traditionally been used for medical, nutritional, and even artisanal purposes. Currently, an increasing interest is granted to these species because of their high content in bioactive compounds (primary and secondary metabolites) such as polyunsaturated fatty acids, carotenoids, vitamins, sterols, essential oils (terpenes), polysaccharides, glycosides, and phenolic compounds. These bioactive substances display potent antioxidant, antimicrobial, anti-inflammatory, and anti-tumoral activities, and therefore represent key-compounds in preventing various diseases (e.g. cancer, chronic inflammation, atherosclerosis and cardiovascular disorder) and ageing processes. The ongoing research will lead to the utilisation of halophytes as a new source of healthy products as functional foods, nutraceuticals or active principles in several industries. This contribution focuses on the ethnopharmacological uses of halophytes in traditional medicine and reviews recent investigations on their biological activities and nutraceuticals. The work is distributed according to the different families of nutraceuticals (lipids, vitamins, proteins, glycosides, phenolic compounds, etc.) discussing the analytical techniques employed for their determination. Information about the claimed health promoting effects of the different families of nutraceuticals is also provided together with data on their application.

Medicinal halophytes: potent source of health promoting biomolecules with medical, nutraceutical and food applications.

Learning from Evolution: Thellungiella Generates New Knowledge on Essential and Critical Components of Abiotic Stress Tolerance in Plants

The phytoalexins from cauliflower, caulilexins A, B and C: isolation, structure determination, syntheses and antifungal activity.

Phytoalexins and phytoanticipins from the wild crucifers Thellungiella halophila and Arabidopsis thaliana: rapalexin A, wasalexins and camalexin.

The biosynthetic pathway of crucifer phytoalexins and phytoanticipins: De novo incorporation of deuterated tryptophans and quasi-natural compounds

Detection, characterization and identification of crucifer phytoalexins using high-performance liquid chromatography with diode array detection and electrospray ionization mass spectrometry.

Adewale M. Adio

Papers

The phytoalexins from cauliflower, caulilexins A, B and C: isolation, structure determination, syntheses and antifungal activity.

Phytoalexins and phytoanticipins from the wild crucifers Thellungiella halophila and Arabidopsis thaliana: rapalexin A, wasalexins and camalexin.

The biosynthetic pathway of crucifer phytoalexins and phytoanticipins: De novo incorporation of deuterated tryptophans and quasi-natural compounds

Detection, characterization and identification of crucifer phytoalexins using high-performance liquid chromatography with diode array detection and electrospray ionization mass spectrometry.

Photochemical dimerization of wasalexins in UV-irradiated Thellungiella halophila and in vitro generates unique cruciferous phytoalexins.