Dihydroflavonol-4-reductase (DFR; EC1.1.1.219) catalyzes a key step late in the biosynthesis of anthocyanins, condensed tannins (proanthocyanidins), and other flavonoids important to plant survival and human nutrition. Two DFR cDNA clones (MtDFR1 and MtDFR2) were isolated from the model legume Medicago truncatula cv Jemalong. Both clones were functionally expressed in Escherichia coli, confirming that both encode active DFR proteins that readily reduce taxifolin (dihydroquercetin) to leucocyanidin. M. truncatula leaf anthocyanins were shown to be cyanidin-glucoside derivatives, and the seed coat proanthocyanidins are known catechin and epicatechin derivatives, all biosynthesized from leucocyanidin. Despite high amino acid similarity (79% identical), the recombinant DFR proteins exhibited differing pH and temperature profiles and differing relative substrate preferences. Although no pelargonidin derivatives were identified in M. truncatula, MtDFR1 readily reduced dihydrokaempferol, consistent with the presence of an asparagine residue at a location known to determine substrate specificity in other DFRs, whereas MtDFR2 contained an aspartate residue at the same site and was only marginally active on dihydrokaempferol. Both recombinant DFR proteins very efficiently reduced 5-deoxydihydroflavonol substrates fustin and dihydrorobinetin, substances not previously reported as constituents of M. truncatula. Transcript accumulation for both genes was highest in young seeds and flowers, consistent with accumulation of condensed tannins and leucoanthocyanidins in these tissues. MtDFR1 transcript levels in developing leaves closely paralleled leaf anthocyanin accumulation. Overexpression of MtDFR1 in transgenic tobacco (Nicotiana tabacum) resulted in visible increases in anthocyanin accumulation in flowers, whereas MtDFR2 did not. The data reveal unexpected properties and differences in two DFR proteins from a single species.Flavonoids represent a large group of plant secondary metabolites with diverse biological activities, and the biochemical and genetic investigations of flavonoid biosynthesis have been well documented (Hahlbrock and Grisebach, 1975;Harborne, 1988;Stafford, 1990;Holton and Cornish, 1995;Dixon and Steele, 1999;Winkel-Shirley, 2001). Flavonoids are divided into several structural classes, including anthocyanins, which provide flower and leaf colors, catechins, and condensed tannins (CTs; proanthocyanidins), which contribute to resistance to microbes, and other derivatives with diverse roles in plant development and interactions with the environment (Harborne, 1988;Dixon and Paiva, 1995;Paiva, 2000). Several flavonoids are active ingredients in herbal medicines and appear to confer health benefits to humans when consumed regularly. Particular attention has been placed on the anthocyanins, catechins, and proanthocyanidins because of their antioxidant activities and their interactions with proteins (Tanner et al., 1994;Scalbert and Williamson, 2000;Ross and Kasum, 2002;Hou, 2003).The common precursors in the ...

Staphylococcus aureus uses several efficient iron acquisition strategies to overcome iron limitation. Recently, the genetic locus encoding biosynthetic enzymes for the iron chelating molecule, staphyloferrin A (SA), was determined. S. aureus synthesizes and secretes SA into its environment to scavenge iron. The membrane-anchored ATP binding cassette-binding protein, HtsA, receives the ferric-chelate for import into the cell. Recently, we determined the apoHtsA crystal structure, the first siderophore receptor from Gram-positive bacteria to be structurally characterized. Herein we present the x-ray crystal structure of the HtsA-ferric-SA complex. HtsA adopts a class III binding protein fold composed of separate N-and C-terminal domains bridged by a single ␣-helix. Recombinant HtsA can efficiently sequester ferric-SA from S. aureus culture supernatants where it is bound within the pocket formed between distinct N-and C-terminal domains. A basic patch composed mainly of six Arg residues contact the negatively charged siderophore, securing it within the pocket. The x-ray crystal structures from two different ligand-bound crystal forms were determined. The structures represent the first structural characterization of an endogenous ␣-hydroxycarboxylate-type siderophore-receptor complex. One structure is in an open form similar to apoHtsA, whereas the other is in a more closed conformation. The conformational change is highlighted by isolated movement of three loops within the C-terminal domain, a domain movement unique to known class III binding protein structures.

Simple sequence repeat (SSR) markers are highly informative and widely used for genetic and breeding studies. Currently, a very limited number of SSR markers are available for tall fescue (Festuca arundinacea Schreb.) and other forage grass species. A tall fescue genomic library enriched in (GA/CT)( n ) repeats was used to develop primer pairs (PPs) flanking SSRs and assess PP functionality across different forage, cereal, and turf grass species. A total of 511 PPs were developed and assessed for their utility in six different grass species. The parents and a subset of a tall fescue mapping population were used to select PPs for mapping in tall fescue. Survey results revealed that 48% (in rice) to 66% (in tall fescue) of the PPs produced clean SSR-type amplification products in different grass species. Polymorphism rates were higher in tall fescue (68%) compared to other species (46% ryegrass, 39% wheat, and 34% rice). A set of 194 SSR loci (38%) were identified which amplified across all six species. Loci segregating in the tall fescue mapping population were grouped as loci segregating from the female parent (HD28-56, 37%), the male parent (R43-64, 37%), and both parents (26%). Three percent of the loci that were polymorphic between parents were monomorphic in the pseudo F1 mapping population and the remaining loci segregated. Sequencing of amplified products obtained from PP NFFAG428 revealed a very high level of sequence similarity among the grass species under study. Our results are the first report of genomic SSR marker development from tall fescue and they demonstrate the usefulness of these SSRs for genetic linkage mapping in tall fescue and cross-species amplification.

This method for estimating clinically important amino acids in serum or urine within 40 min involves o-phthalaldehyde/2-mercaptoethanol derivatization and reversed-phase "high-pressure" liquid chromatography. Homocysteic acid is an internal standard, and homoserine and norvaline are reference peaks. For all the amino acids estimated, the between-run coefficients of variation ranged from 2.0 to 13.5%, and the mean analytical recoveries from both serum and urine samples was 101%. Peak areas vary linearly with concentration up to 1500 mumol/L for all the amino acids assayed. The limit of detection for each amino acid was estimated to be 38 fmol.