Circular dichroism, a powerful tool for the assessment of absolute configuration of flavonoids.

Phytoalexins: enzymology and molecular biology.

Flavonoids are a signature class of secondary metabolites formed from a relatively simple collection of scaffolds. They are extensively decorated by chemical reactions including glycosylation, methylation, and acylation. They are present in a wide variety of fruits and vegetables and as such in Western populations it is estimated that 20-50 mg of flavonoids are consumed daily per person. In planta they have demonstrated to contribute to both flower color and UV protection. Their consumption has been suggested to presenta wide range of health benefits. Recent technical advances allowing affordable whole genome sequencing, as well as a better inventory of species-by-species chemical diversity, have greatly advanced our understanding as to how flavonoid biosynthesis pathways vary across species. In parallel, reverse genetics combined with detailed molecular phenotyping is currently allowing us to elucidate the functional importance of individual genes and metabolites and by this means to provide further mechanistic insight into their biological roles. Here we provide an inventory of current knowledge of pathways of flavonoid biosynthesis in both the model plant Arabidopsis thaliana and a range of crop species, including tomato, maize, rice, and bean.

Current understanding of the pathways of flavonoid biosynthesis in model and crop plants

There are marked differences in the pattern of host gene expression in incompatible plant: microbial pathogen interactions compared with compatible interactions, associated with the elaboration of inducible defenses Constitutive expression of genes encoding a chitinase or a ribosome-inactivating protein in transgenic plants confers partial protection against fungal attack, and a large repertoire of such antimicrobial genes has been identified for further manipulation In addition, strategies are emerging for the manipulation of multigenic defenses such as lignin deposition and synthesis of phytoalexin antibiotics by overexpression of genes encoding rate determining steps, modification of transcription factors or other regulatory genes, and engineering production of novel phytoalexins by interspecies transfer of biosynthetic genes The imminent cloning of disease resistance genes, futher molecular dissection of stress signal perception and transduction mechanisms, and identification of genes that affect symptom development will provide attractive new opportunities for enhancing crop protection Combinatorial integration of these novel strategies into ongoing breeding programs should make an important contribution to effective, durable field resistance

Emerging Strategies for Enhancing Crop Resistance to Microbial Pathogens

Identification of Isoflavone Metabolites Dihydrodaidzein, Dihydrogenistein, 6′-OH-O-dma, and cis-4-OH-equol in Human Urine by Gas Chromatography–Mass Spectroscopy Using Authentic Reference Compounds

Phaseollin formation and metabolism in Phaseolus vulgaris

Phaseoluteone and other 5-hydroxyisoflavonoids from phaseolus vulgaris

New isoflavonoids related to kievitone from Phaseolus vulgaris

White clover leaflets were inoculated with a spore suspension of Monilinia fructicola and the principal isoflavonoids found at 40 h were medicarpin and demethylmedicarpin, a fungal-mediated conversion product of medicarpin. These compounds were identified by gas-liquid chromatography-mass spectrometry (g.l.c./m.s.) of their trimethylsilyl ethers using a column of 1·5% OV-101. G.l.c./m.s. with single ion monitoring was used to detect the trimethylsilyl ethers of several minor isoflavonoids in the extract. After thin layer chromatographic fractionation of the compounds in the extract, g.l.c./ m.s. was used with single ion detection and repetitive scanning over a narrow mass range to confirm the presence of formononetin (7-hydroxy-4′-methoxyisoflavone), 2′hydroxyformononetin and vestitone (7,2′-dihydroxy-4′-methoxyisoflavanone) in the fractions obtained from the extract. The identification of these 3 isoflavonoids from the extract provides further evidence for the biosynthetic pathway leading to medicarpin which was proposed based on the incorporation of radiolabelled precursors into medicarpin.

Michael D. Woodward

Papers

Phaseollin formation and metabolism in Phaseolus vulgaris

Phaseoluteone and other 5-hydroxyisoflavonoids from phaseolus vulgaris

New isoflavonoids related to kievitone from Phaseolus vulgaris

Identification of the biosynthetic precursors of medicarpin in inoculation droplets on white clover

Differentiation of dihydroxy-monomethoxyisoflavones by gas chromatography-mass spectroscopy