Topic
Phytoalexin
About: Phytoalexin is a research topic. Over the lifetime, 1161 publications have been published within this topic receiving 63405 citations. The topic is also known as: phytoalexins.
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TL;DR: It is reported that MPK3/MPK6 and their substrate ERF6 promote the biosynthesis of IGSs and the conversion of I3G to 4MI3G, a target of PEN2/PEN3-dependent chemical defenses in plant immunity.
Abstract: Antimicrobial compounds have critical roles in plant immunity; for example, Arabidopsis thaliana and other crucifers deploy phytoalexins and glucosinolate derivatives in defense against pathogens. The pathogen-responsive MITOGEN-ACTIVATED PROTEIN KINASE3 (MPK3) and MPK6 have essential functions in the induction of camalexin, the major phytoalexin in Arabidopsis. In search of cyanide, a coproduct of ethylene and camalexin biosynthesis, we found that MPK3 and MPK6 also affect the accumulation of extracellular thiocyanate ion derived from the indole glucosinolate (IGS) pathway. Botrytis cinerea infection activates MPK3/MPK6, which promote indole-3-yl-methylglucosinolate (I3G) biosynthesis and its conversion to 4-methoxyindole-3-yl-methylglucosinolate (4MI3G). Gain- and loss-of-function analyses demonstrated that MPK3/MPK6 regulate the expression of MYB51 and MYB122, two key regulators of IGS biosynthesis, as well as CYP81F2 and IGMT1/IGMT2, which encode enzymes in the conversion of I3G to 4MI3G, through ETHYLENE RESPONSE FACTOR6 (ERF6), a substrate of MPK3/MPK6. Under the action of PENETRATION2 (PEN2), an atypical myrosinase, and PEN3, an ATP binding cassette transporter, 4MI3G is converted to extracellular unstable antimicrobial compounds, possibly isothiocyanates that can react with nucleophiles and release the stable thiocyanate ion. Recent studies demonstrated the importance of PEN2/PEN3-dependent IGS derivatives in plant immunity. Here, we report that MPK3/MPK6 and their substrate ERF6 promote the biosynthesis of IGSs and the conversion of I3G to 4MI3G, a target of PEN2/PEN3-dependent chemical defenses in plant immunity.
112 citations
TL;DR: Detailed evidence is provided that, during early colonization of plant roots by symbiotic Glomus, defense transcripts are induced and then subsequently suppressed and this work supply detailed evidence that suppression of the host defense response is regulated by changes in the steady-state mRNA level.
Abstract: Isoflavonoids and steady-state mRNA levels of phenylalanine ammonia-lyase, chalcone isomerase, and isoflavone reductase were followed during a rapid, nearly synchronous infection of alfalfa (Medicago sativa L.) roots by the vesicular arbuscular fungus Glomus intraradices (Schenck & Smith) to test whether previously indicated suppression of the host defense response is regulated by changes in the steady-state mRNA level. Relative amounts of steady-state phenylalanine ammonia-lyase mRNA in the mycorrhizal roots doubled between d 14 and 18 and then immediately declined by 75% to reach and maintain a value lower than the control roots through d 21. Relative levels of chalcone isomerase mRNA in the inoculated roots increased 6-fold between d 14 and 17 and then decreased rapidly to the control level. Isoflavone reductase mRNA was not induced by mycorrhizal colonization. High-performance liquid chromatography, proton-nuclear magnetic resonance, and fast atom bombardment-mass spectrometry analyses showed consistent increases in formononetin levels and transient increases in medicarpin-3-O-glycoside and formononetin conjugates in the inoculated roots when colonization began. As colonization increased, levels of formononetin conjugates declined in mycorrhizal roots below those in uncolonized controls. Medicarpin aglycone, an alfalfa phytoalexin normally associated with pathogenic infections, was not detected at any stage. These findings supply detailed evidence that, during early colonization of plant roots by symbiotic Glomus, defense transcripts are induced and then subsequently suppressed.
111 citations
TL;DR: A suggested mode of action of this elicitor in the plant in which fragments of the plant cell wall released through the catalytic action of the enzyme serve as secondary elicitors to trigger the plant response is proposed on the basis of preliminary observations.
Abstract: Several types of fungal molecules including cell wall polysaccharides, polypeptides, glycoproteins and lipid molecules have been found to serve as elicitors of phytoalexins in higher plants. Recent work has shown that an extracellular enzyme, endopolygalacturonase, from culture filtrates of the fungusRhizopus stolonifer elicits the biosynthesis of an antifungal antibiotic, casbene, in extracts of treated castor bean (Ricinus communis L.) seedlings. A suggested mode of action of this elicitor in the plant in which fragments of the plant cell wall released through the catalytic action of the enzyme serve as secondary elicitors to trigger the plant response is proposed on the basis of preliminary observations. Possible modes of interaction of other types of fungal elicitors with plants are also discussed.
110 citations
TL;DR: Analysis of soybean membranes suggested that the putative glucan‐elicitor receptors bind a basic structural determinant present in all elicitor‐active glucans from the soybean pathogen P. megasperma.
110 citations
TL;DR: The pterocarpan phytoalexins of the Leguminosae are synthesized from L-phenyl-alanine via a minimum of 11 enzymatic steps involving the central phenylpropanoid pathway, three reactions of flavonoid biosynthesis, and the isoflavonoid branch pathway.
Abstract: The pterocarpan phytoalexins of the Leguminosae are synthesized from L-phenyl-alanine via a minimum of 11 enzymatic steps involving the central phenylpropanoid pathway, three reactions of flavonoid biosynthesis, and the isoflavonoid branch pathway. The extractable activities of all these enyzmes, and of enzymes supplying precursors from primary metabolism, increase in response to fungal infection or exposure of plant cells to elicitor macromolecules isolated from the cell walls of yeast or plant pathogenic fungi. The involvement of reductases and cytochrome P450 hydroxylases places a high demand for NADPH on elicited cells. The NADPH is most likely supplied by activation of the pentose phosphate pathway. Genes or cDNAs encoding 7 of the enzymes involved in the synthesis of the phytoalexin medicarpin have been cloned from alfalfa and/or other species. Induction of enzyme activity results from transcriptional activation of the corresponding genes, leading to increased steady state levels of translatable mRNAs. This transcriptional activation is programmed through the interaction of sets of elicitor/infection-modulated transcription factors with their cognate cis elements in the promoters of the phytoalexin biosynthetic genes. Gene activation occurs through generation of intracellular signals which lead to modulation of transcription factor activity, through either increased synthesis of the factor(s), activation via reversible post-translational modification (e.g. phosphorylation/dephos-phorylation), translocation of factors from cytoplasm to nucleus, or combinations of these. Coordinated induction of the enzymes of phytoalexin synthesis may involve multiple signals and factors for transcriptional activation, as well as feedback and feed-forward fine controls at both transcriptional and post-transcriptional levels. In beneficial mycorrhizal interactions, induction of early pathway genes is uncoupled from that of later, phytoalexin-specific genes.
108 citations