camalexin and indole-3-carboxylic-acid

In plants, a host's responses to an attempted infection include activation of various secondary metabolite pathways, some of which are specific for particular plant phylogenetic clades. Phytochemicals that represent respective end products in plant immunity have been stereotypically linked to antimicrobial properties. However, in many cases, owing to the lack of unequivocal evidence for direct antibiotic action in planta, alternative functions of secondary metabolites should be considered. Correspondingly, recent findings have identified novel, and rather unexpected, functions of phytochemicals in plant immunity that mediate regulatory pathways for conserved defence responses. It also seems likely that these conserved responses can be regulated by clade-specific phytochemicals.

Topics: Anti-Infective Agents; ATP-Binding Cassette Transporters; Bacteria; Benzoxazines; Cell Wall; Chemical Warfare Agents; Fungi; Glucosinolates; Host-Pathogen Interactions; Indoles; Isothiocyanates; Plant Immunity; Plants; Thiazoles

Nonhost resistance of Arabidopsis thaliana against the hemibiotrophic fungus Colletotrichum tropicale requires PEN2-dependent preinvasive resistance and CYP71A12 and CYP71A13-dependent postinvasive resistance, which both rely on tryptophan (Trp) metabolism. We here revealed that CYP71A12, CYP71A13 and PAD3 are critical for Arabidopsis' postinvasive basal resistance toward the necrotrophic Alternaria brassicicola. Consistent with this, gene expression and metabolite analyses suggested that the invasion by A. brassicicola triggered the CYP71A12-dependent production of indole-3-carboxylic acid derivatives and the PAD3 and CYP71A13-dependent production of camalexin. We next addressed the activation of the CYP71A12 and PAD3-dependent postinvasive resistance. We found that bak1-5 mutation significantly reduced postinvasive resistance against A. brassicicola, indicating that pattern recognition contributes to activation of this second defense-layer. However, the bak1-5 mutation had no detectable effects on the Trp-metabolism triggered by the fungal penetration. Together with this, further comparative gene expression analyses suggested that pathogen invasion in Arabidopsis activates (1) CYP71A12 and PAD3-related antifungal metabolism that is not hampered by bak1-5, and (2) a bak1-5 sensitive immune pathway that activates the expression of antimicrobial proteins.

Topics: Alternaria; Arabidopsis; Arabidopsis Proteins; Cytochrome P-450 Enzyme System; Disease Resistance; Gene Expression Regulation, Plant; Indoles; Plant Diseases; Protein Serine-Threonine Kinases; Thiazoles; Tryptophan

Indole-3-carboxylic acid (I3CA) is an indolic compound that induces resistance in Arabidopsis adult plants against the necrotrophic fungus

Topics: Arabidopsis; Ascomycota; Biosynthetic Pathways; Disease Resistance; Glucans; Indoles; Plant Diseases; Thiazoles

Tryptophan-derived, indolic metabolites possess diverse functions in Arabidopsis innate immunity to microbial pathogen infection. Here, we investigate the functional role and regulatory characteristics of indolic metabolism in Arabidopsis systemic acquired resistance (SAR) triggered by the bacterial pathogen Pseudomonas syringae. Indolic metabolism is broadly activated in both P. syringae-inoculated and distant, non-inoculated leaves. At inoculation sites, camalexin, indol-3-ylmethylamine (I3A), and indole-3-carboxylic acid (ICA) are the major accumulating compounds. Camalexin accumulation is positively affected by MYB122, and the cytochrome P450 genes CYP81F1 and CYP81F2. Local I3A production, by contrast, occurs via indole glucosinolate breakdown by PEN2- dependent and independent pathways. Moreover, exogenous application of the defense hormone salicylic acid stimulates I3A generation at the expense of its precursor indol-3-ylmethylglucosinolate (I3M), and the SAR regulator pipecolic acid primes plants for enhanced P. syringae-induced activation of distinct branches of indolic metabolism. In uninfected systemic tissue, the metabolic response is more specific and associated with enhanced levels of the indolics I3A, ICA, and indole-3-carbaldehyde (ICC). Systemic indole accumulation fully depends on functional CYP79B2/3, PEN2, and MYB34/51/122, and requires functional SAR signaling. Genetic analyses suggest that systemically elevated indoles are dispensable for SAR and associated systemic increases of salicylic acid. However, soil-grown but not hydroponically -cultivated cyp79b2/3 and pen2 plants, both defective in indolic secondary metabolism, exhibit pre-induced immunity, which abrogates their intrinsic ability to induce SAR.

Topics: Arabidopsis; Disease Resistance; Gene Expression Regulation, Plant; Immunity, Innate; Indoles; Plant Diseases; Pseudomonas syringae; Thiazoles

Camalexin (3-thiazol-2'-yl-indole) is the major phytoalexin found in Arabidopsis thaliana. Several key intermediates and corresponding enzymes have been identified in camalexin biosynthesis through mutant screening and biochemical experiments. Camalexin is formed when indole-3-acetonitrile (IAN) is catalyzed by the cytochrome P450 monooxygenase CYP71A13. Here, we demonstrate that the Arabidopsis GH3.5 protein, a multifunctional acetyl-amido synthetase, is involved in camalexin biosynthesis via conjugating indole-3-carboxylic acid (ICA) and cysteine (Cys) and regulating camalexin biosynthesis genes. Camalexin levels were increased in the activation-tagged mutant gh3.5-1D in both Col-0 and cyp71A13-2 mutant backgrounds after pathogen infection. The recombinant GH3.5 protein catalyzed the conjugation of ICA and Cys to form a possible intermediate indole-3-acyl-cysteinate (ICA(Cys)) in vitro. In support of the in vitro reaction, feeding with ICA and Cys increased camalexin levels in Col-0 and gh3.5-1D. Dihydrocamalexic acid (DHCA), the precursor of camalexin and the substrate for PAD3, was accumulated in gh3.5-1D/pad3-1, suggesting that ICA(Cys) could be an additional precursor of DHCA for camalexin biosynthesis. Furthermore, expression of the major camalexin biosynthesis genes CYP79B2, CYP71A12, CYP71A13 and PAD3 was strongly induced in gh3.5-1D. Our study suggests that GH3.5 is involved in camalexin biosynthesis through direct catalyzation of the formation of ICA(Cys), and upregulation of the major biosynthetic pathway genes.

Topics: Arabidopsis; Arabidopsis Proteins; Cysteine; Cytochrome P-450 Enzyme System; Indoles; Ligases; Plants, Genetically Modified; Thiazoles

The chemical structures and accumulation kinetics of several major soluble as well as wall-bound, alkali-hydrolyzable compounds induced upon infection of Arabidopsis thaliana leaves with Pseudomonas syringae pathovar tomato were established. All identified accumulating products were structurally related to tryptophan. Most prominent among the soluble substances were tryptophan, beta-d-glucopyranosyl indole-3-carboxylic acid, 6-hydroxyindole-3-carboxylic acid 6-O-beta-d-glucopyranoside, and the indolic phytoalexin camalexin. The single major accumulating wall component detectable under these conditions was indole-3-carboxylic acid. All of these compounds increased more rapidly, and camalexin as well as indole-3-carboxylic acid reached much higher levels, in the incompatible than in the compatible P. syringae/A. thaliana interaction. The only three prominent phenylpropanoid derivatives present in the soluble extract behaved differently. Two kaempferol glycosides remained largely unaffected, and sinapoyl malate decreased strongly upon bacterial infection with a time course inversely correlated with that of the accumulating tryptophan-related products. The accumulation patterns of both soluble and wall-bound compounds, as well as the disease resistance phenotypes, were essentially the same for infected wild-type and tt4 (no kaempferol glycosides) or fah1 (no sinapoyl malate) mutant plants. Largely different product combinations accumulated in wounded or senescing A. thaliana leaves. It seems unlikely that any one of the infection-induced compounds identified so far has a decisive role in the resistance response to P. syringae.

Topics: Arabidopsis; Arabidopsis Proteins; Cell Wall; Cytochrome P-450 Enzyme System; Cytosol; Flavonoids; Glycosides; Indoles; Kaempferols; Malates; Mixed Function Oxygenases; Phenylpropionates; Plant Leaves; Plant Proteins; Pseudomonas; Quercetin; Solubility; Thiazoles; Tryptophan; Virulence