Development of microsatellite markers for sunflower (Helianthus annuus L.) was performed to estimate their frequency, nature (structure), levels of polymorphism, usefulness for genotype identification, and calculation of genetic relationships between inbred lines representing the species diversity. Isolation was performed from a small-insert genomic library followed by hybridization screening using oligonucleotide probes containing different nucleotide arrays. In this work, 503 unique microsatellite clones were sequenced and 271 PCR primer sequences bordering the microsatellite repeat were designed. For polymorphism assessment, 16 H. annuus germplasm accessions were checked and 170 of the primers tested were shown to be polymorphic for the selected lines. The polymorphic microsatellites produced an average of 3.5 alleles/locus and an average polymorphism information content (PIC) of 0.55. The most frequently found motifs within polymorphic simple-sequence repeats (SSRs) were: (GA)n, (GT)n, (AT)n, followed by trinucleotides (ATT)n, (TGG)n, and (ATC)n, and the tetranucleotide (CATA)n. Most of the 170 SSRs obtained showed important differences in the 16 reference inbred lines used for their characterization. In this work, 20 of the most informative SSRs destined to sunflower genotyping and legal fingerprinting purposes are fully described.

BackgroundArgentina has a long tradition of sunflower breeding, and its germplasm is a valuable genetic resource worldwide. However, knowledge of the genetic constitution and variability levels of the Argentinean germplasm is still scarce, rendering the global map of cultivated sunflower diversity incomplete. In this study, 42 microsatellite loci and 384 single nucleotide polymorphisms (SNPs) were used to characterize the first association mapping population used for quantitative trait loci mapping in sunflower, along with a selection of allied open-pollinated and composite populations from the germplasm bank of the National Institute of Agricultural Technology of Argentina. The ability of different kinds of markers to assess genetic diversity and population structure was also evaluated.ResultsThe analysis of polymorphism in the set of sunflower accessions studied here showed that both the microsatellites and SNP markers were informative for germplasm characterization, although to different extents. In general, the estimates of genetic variability were moderate. The average genetic diversity, as quantified by the expected heterozygosity, was 0.52 for SSR loci and 0.29 for SNPs. Within SSR markers, those derived from non-coding regions were able to capture higher levels of diversity than EST-SSR. A significant correlation was found between SSR and SNP- based genetic distances among accessions. Bayesian and multivariate methods were used to infer population structure. Evidence for the existence of three different genetic groups was found consistently across data sets (i.e., SSR, SNP and SSR + SNP), with the maintainer/restorer status being the most prevalent characteristic associated with group delimitation.ConclusionThe present study constitutes the first report comparing the performance of SSR and SNP markers for population genetics analysis in cultivated sunflower. We show that the SSR and SNP panels examined here, either used separately or in conjunction, allowed consistent estimations of genetic diversity and population structure in sunflower breeding materials. The generated knowledge about the levels of diversity and population structure of sunflower germplasm is an important contribution to this crop breeding and conservation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0360-x) contains supplementary material, which is available to authorized users.

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Phlorisovalerophenone synthase (VPS), a novel aromatic polyketide synthase, was purified to homogeneity from 4.2 mg protein extract obtained from hop (Humulus lupulus L.) cone glandular hairs. The enzyme uses isovaleryl-CoA or isobutyryl-CoA and three molecules of malonyl-CoA to form phlorisovalerophenone or phlorisobutyrophenone, intermediates in the biosynthesis of the hop bitter acids (a-and b-acids). VPS is an homodimeric enzyme, with subunits of 45 kDa. The pI of the enzyme was 6.1. K m values of 4 mm for isovaleryl-CoA, 10 mm for isobutyryl-CoA and 33 mm for malonyl-CoA, were found. The amino-acid sequences of two peptides, obtained by digestion of VPS, showed that the enzyme is highly homologous to plant chalcone synthases. The functional and structural relationship between VPS and other aromatic polyketide synthases is discussed.Keywords: Humulus lupulus; chalcone synthase; polyketide synthase; hop bitter acids; phlorisovalerophenone synthase.The cones of the hop plant (Humulus lupulus L.) have been used for centuries in the beer-brewing process. Their major contribution to beer is the characteristic bitterness that results from the isomerization of the hop a-acids into a more soluble and stable form during the brewing process; isomerized a-acids are the main bitter substances in beer. In the plant, hop bitter acids consist of both a-acids, mainly humulone, cohumulone and adhumulone, and b-acids, mainly lupulone, colupulone and adlupulone [1]. These compounds are synthesized during the development of the H. lupulus female inflorescences into cones and are accumulated in the yellow glands covering the basal part of the bracteoles of the cones [2,3]. In general, glands are a rich source of secondary metabolites. Recently, strategies for bioengineering the development and metabolism in glandular tissues have been reviewed [4].In previous papers [5,6] a novel biosynthetic pathway leading to the bitter acids in H. lupulus was proposed. The suggested intermediates phlorisovalerophenone and phlorisobutyrophenone were also detected in hop cones. Furthermore, protein extracts from the cones were able to synthesize these compounds from malonyl-CoA plus either isovaleryl-CoA or isobutyryl-CoA. Apparently, the catalytic mechanism involved in this biosynthesis is similar to that observed in other plant condensing enzymes, like chalcone synthase and stilbene synthase (Fig. 1). These enzymes catalyze a reaction which proceeds by a sequential condensation of three acetate units to a starter residue to form the tetraketide intermediate that is folded to form a ring [7,8]. This type of reaction, which was first described by Birch and Donovan [9], classifies chalcone synthase and stilbene synthase as polyketide synthases. Chalcone synthase is a key enzyme in the biosynthesis of flavonoids. It catalyzes the formation of naringenin from three molecules of malonyl-CoA and coumaroyl-CoA. Stilbene synthase, an enzyme in the biosynthesis of stilbene phytoalexins, is structurally and functionally related to chalcone synthase. Usi...