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Background: Solanum dulcamara (bittersweet, climbing nightshade) is one of the few species of the Solanaceae family native to Europe. As a common weed it is adapted to a wide range of ecological niches and it has long been recognized as one of the alternative hosts for pathogens and pests responsible for many important diseases in potato, such as Phytophthora. At the same time, it may represent an alternative source of resistance genes against these diseases. Despite its unique ecology and potential as a genetic resource, genomic research tools are lacking for S. dulcamara. We have taken advantage of next-generation sequencing to speed up research on and use of this non-model species., Results: In this work, we present the first large-scale characterization of the S. dulcamara transcriptome. Through comparison of RNAseq reads from two different accessions, we were able to predict transcript-based SNP and SSR markers. Using the SNP markers in combination with genomic AFLP and CAPS markers, the first genome-wide genetic linkage map of bittersweet was generated. Based on gene orthology, the markers were anchored to the genome of related Solanum species (tomato, potato and eggplant), revealing both conserved and novel chromosomal rearrangements. This allowed a better estimation of the evolutionary moment of rearrangements in a number of cases and showed that chromosomal breakpoints are regularly re-used., Conclusion: Knowledge and tools developed as part of this study pave the way for future genomic research and exploitation of this wild Solanum species. The transcriptome assembly represents a resource for functional analysis of genes underlying interesting biological and agronomical traits and, in the absence of the full genome, provides a reference for RNAseq gene expression profiling aimed at understanding the unique biology of S. dulcamara. Cross-species orthology-based marker selection is shown to be a powerful tool to quickly generate a comparative genetic map, which may speed up gene mapping and contribute to the understanding of genome evolution within the Solanaceae family.

The H1 locus confers resistance to the potato cyst nematode Globodera rostochiensis pathotypes 1 and 4. It is positioned at the distal end of chromosome V of the diploid Solanum tuberosum genotype SH83-92-488 (SH) on an introgression segment derived from S. tuberosum ssp. andigena. Markers from a high-resolution genetic map of the H1 locus (Bakker et al. in Theor Appl Genet 109:146-152, 2004) were used to screen a BAC library to construct a physical map covering a 341-kb region of the resistant haplotype coming from SH. For comparison, physical maps were also generated of the two haplotypes from the diploid susceptible genotype RH89-039-16 (S. tuberosum ssp. tuberosum/S. phureja), spanning syntenic regions of 700 and 319 kb. Gene predictions on the genomic segments resulted in the identification of a large cluster consisting of variable numbers of the CC-NB-LRR type of R genes for each haplotype. Furthermore, the regions were interspersed with numerous transposable elements and genes coding for an extensin-like protein and an amino acid transporter. Comparative analysis revealed a major lack of gene order conservation in the sequences of the three closely related haplotypes. Our data provide insight in the evolutionary mechanisms shaping the H1 locus and will facilitate the map-based cloning of the H1 resistance gene.

Isoguanosine-5'-pyrosphosphate, in the presence of an oligonucleotide primer, was polymerized by Escherichia coli polynucleotide phosphorylase under conditions analogous to those required for polymerization of 5'-GMP. The resulting poly(isoguanylic acid), poly(isoG), was a multistranded helix with a stability considerably higher than that of poly(G), and fully resistant to various nucleolytic enzymes. The polymer exhibited a two-step temperature transition profile in moderately alkaline propylene glycol. Alkaline titration in aqueous medium, by ultraviolet and circular dichroism spectroscopy, showed two clearly defined transitions, the second of which was fully cooperative. The accompanying changes in sedimentation constants were consistent with a structure for poly(isoG) of a fourstranded helix, like neutral poly(G). In acid medium, spectral and potentiometric titrations demonstrated the existence of more than one transition in the pH range 6-12, with accompanying protonation of the isoguanosine residues. In neutral medium the polymer formed no complexes with other potentially complementary homopolymers. In acid medium, on the other hand, the protonated form of poly(isoG) did form a triple-stranded complex with poly(I), viz. 2poly(I) . poly(isoG)+. Possible structures are formulated for the neural and protonated forms of poly(isoG) which account for the two-step thermal transition in alkaline propylene glycol and on alkaline titration in aqueous medium. The nature of the protonated form, and its complex with poly(I) is also discussed.