Developing molecular tools and insights into the Penstemon genome using genomic reduction and next-generation sequencing.

BACKGROUND: Penstemon's unique phenotypic diversity, hardiness, and drought-tolerance give it great potential for the xeric landscaping industry. Molecular markers will accelerate the breeding and domestication of drought tolerant Penstemon cultivars by, creating genetic maps, and clarifying of phylogenetic relationships. Our objectives were to identify and validate interspecific molecular markers from four diverse Penstemon species in order to gain specific insights into the Penstemon genome. RESULTS: We used a 454 pyrosequencing and GR-RSC (genome reduction using restriction site conservation) to identify homologous loci across four Penstemon species (P. cyananthus, P. davidsonii, P. dissectus, and P. fruticosus) representing three diverse subgenera with considerable genome size variation. From these genomic data, we identified 133 unique interspecific markers containing SSRs and INDELs of which 51 produced viable PCR-based markers. These markers produced simple banding patterns in 90% of the species × marker interactions (~84% were polymorphic). Twelve of the markers were tested across 93, mostly xeric, Penstemon taxa (72 species), of which ~98% produced reproducible marker data. Additionally, we identified an average of one SNP per 2,890 bp per species and one per 97 bp between any two apparent homologous sequences from the four source species. We selected 192 homologous sequences, meeting stringent parameters, to create SNP markers. Of these, 75 demonstrated repeatable polymorphic marker functionality across the four sequence source species. Finally, sequence analysis indicated that repetitive elements were approximately 70% more prevalent in the P. cyananthus genome, the largest genome in the study, than in the smallest genome surveyed (P. dissectus). CONCLUSIONS: We demonstrated the utility of GR-RSC to identify homologous loci across related Penstemon taxa. Though PCR primer regions were conserved across a broadly sampled survey of Penstemon species (93 taxa), DNA sequence within these amplicons (12 SSR/INDEL markers) was highly diverse. With the continued decline in next-generation sequencing costs, it will soon be feasible to use genomic reduction techniques to simultaneously sequence thousands of homologous loci across dozens of Penstemon species. Such efforts will greatly facilitate our understanding of the phylogenetic structure within this important drought tolerant genus. In the interim, this study identified thousands of SNPs and over 50 SSRs/INDELs which should provide a foundation for future Penstemon phylogenetic studies and breeding efforts.

Single nucleotide polymorphism discovery in cutthroat trout subspecies using genome reduction, barcoding, and 454 pyro-sequencing.

BACKGROUND: Salmonids are popular sport fishes, and as such have been subjected to widespread stocking throughout western North America. Historically, stocking was done with little regard for genetic variation among populations and has resulted in genetic mixing among species and subspecies in many areas, thus putting the genetic integrity of native salmonid populations at risk and creating a need to assess the genetic constitution of native salmonid populations. Cutthroat trout is a salmonid species with pronounced geographic structure (there are 10 extant subspecies) and a recent history of hybridization with introduced rainbow trout in many populations. Genetic admixture has also occurred among cutthroat trout subspecies in areas where introductions have brought two or more subspecies into contact. Consequently, management agencies have increased their efforts to evaluate the genetic composition of cutthroat trout populations to identify populations that remain uncompromised and manage them accordingly, but additional genetic markers are needed to do so effectively. Here we used genome reduction, MID-barcoding, and 454-pyrosequencing to discover single nucleotide polymorphisms that differentiate cutthroat trout subspecies and can be used as a rapid, cost-effective method to characterize the genetic composition of cutthroat trout populations. RESULTS: Thirty cutthroat and six rainbow trout individuals were subjected to genome reduction and next-generation sequencing. A total of 1,499,670 reads averaging 379 base pairs in length were generated by 454-pyrosequencing, resulting in 569,060,077 total base pairs sequenced. A total of 43,558 putative SNPs were identified, and of those, 125 SNP primers were developed that successfully amplified 96 cutthroat trout and rainbow trout individuals. These SNP loci were able to differentiate most cutthroat trout subspecies using distance methods and Structure analyses. CONCLUSIONS: Genomic and bioinformatic protocols were successfully implemented to identify 125 nuclear SNPs that are capable of differentiating most subspecies of cutthroat trout from one another. The ability to use this suite of SNPs to identify individuals of unknown genetic background to subspecies can be a valuable tool for management agencies in their efforts to evaluate the genetic structure of cutthroat trout populations prior to constructing and implementing conservation plans.