Rapid purification of fluorescent dye-labeled products in a 96-well format for high-throughput automated DNA sequencing

No-wash ethanol precipitation of dye-labeled reaction products improves DNA sequencing reads

The advent of DNA sequencing has significantly accelerated molecular biology and clinical genetic testing. Despite recent increases in next-generation sequencing throughput, the most popular platform for DNA sequencing is still the multi-capillary DNA sequencer, which is ideally suited for small-scale sequencing projects and is highly accurate. However, the methods remain time-consuming and laborious. Here, I describe a modified ethylenediaminetetraacetic acid (EDTA) method that skips the washing step in ethanol precipitation. My improvements to standard methods save labor, time, and cost per run and increase the sequence reads by 5 to 10%. This modified method will provide immediate benefits to many researchers.

Transcriptome analysis of leaf tissue from Bermudagrass (Cynodon dactylon) using a normalised cDNA library

A normalised cDNA library was constructed from Bermudagrass to gain insight into the transcriptome of Cynodon dactylon L. A total of 15 588 high-quality expressed sequence tags (ESTs) from the cDNA library were subjected to The Institute for Genomic Research Gene Indices clustering tools to produce a unigene set. A total of 9414 unigenes were obtained from the high-quality ESTs and only 39.6% of the high-quality ESTs were redundant, indicating that the normalisation procedure was effective. A large-scale comparative genomic analysis of the unigenes was carried out using publicly available tools, such as BLAST, InterProScan and Gene Ontology. The unigenes were also subjected to a search for EST-derived simple sequence repeats (EST-SSRs) and conserved-intron scanning primers (CISPs), which are useful as DNA markers. Although the candidate EST-SSRs and CISPs found in the present study need to be empirically tested, they are expected to be useful as DNA markers for many purposes, including comparative genomic studies of grass species, by virtue of their significant similarities to EST sequences from other grasses. Thus, knowledge of Cynodon ESTs will empower turfgrass research by providing homologues for genes that are thought to confer important functions in other plants.

Functional classification, genomic organization, putatively cis-acting regulatory elements, and relationship to quantitative trait loci, of sorghum genes with rhizome-enriched expression

Rhizomes are organs of fundamental importance to plant competitiveness and invasiveness. We have identified genes expressed at substantially higher levels in rhizomes than other plant parts, and explored their functional categorization, genomic organization, regulatory motifs, and association with quantitative trait loci (QTLs) conferring rhizomatousness. The finding that genes with rhizome-enriched expression are distributed across a wide range of functional categories suggests some degree of specialization of individual members of many gene families in rhizomatous plants. A disproportionate share of genes with rhizome-enriched expression was implicated in secondary and hormone metabolism, and abiotic stimuli and development. A high frequency of unknown-function genes reflects our still limited knowledge of this plant organ. A putative oligosaccharyl transferase showed the highest degree of rhizome-specific expression, with several transcriptional or regulatory protein complex factors also showing high (but lesser) degrees of specificity. Inferred by the upstream sequences of their putative rice (Oryza sativa) homologs, sorghum (Sorghum bicolor) genes that were relatively highly expressed in rhizome tip tissues were enriched for cis-element motifs, including the pyrimidine box, TATCCA box, and CAREs box, implicating the gibberellins in regulation of many rhizome-specific genes. From cDNA clones showing rhizome-enriched expression, expressed sequence tags forming 455 contigs were plotted on the rice genome and aligned to QTL likelihood intervals for ratooning and rhizomatous traits in rice and sorghum. Highly expressed rhizome genes were somewhat enriched in QTL likelihood intervals for rhizomatousness or ratooning, with specific candidates including some of the most rhizome-specific genes. Some rhizomatousness and ratooning QTLs were shown to be potentially related to one another as a result of ancient duplication, suggesting long-term functional conservation of the underlying genes. Insight into genes and pathways that influence rhizome growth set the stage for genetic and/or exogenous manipulation of rhizomatousness, and for further dissection of the molecular evolution of rhizomatousness.

An SNP resource for rice genetics and breeding based on subspecies indica and japonica genome alignments

Dense coverage of the rice genome with polymorphic DNA markers is an invaluable tool for DNA marker-assisted breeding, positional cloning, and a wide range of evolutionary studies. We have aligned drafts of two rice subspecies, indica and japonica, and analyzed levels and patterns of genetic diversity. After filtering multiple copy and low quality sequence, 408,898 candidate DNA polymorphisms (SNPs/INDELs) were discerned between the two subspecies. These filters have the consequence that our data set includes only a subset of the available SNPs (in particular excluding large numbers of SNPs that may occur between repetitive DNA alleles) but increase the likelihood that this subset is useful: Direct sequencing suggests that 79.8% +/- 7.5% of the in silico SNPs are real. The SNP sample in our database is not randomly distributed across the genome. In fact, 566 rice genomic regions had unusually high (328 contigs/48.6 Mb/13.6% of genome) or low (237 contigs/64.7 Mb/18.1% of genome) polymorphism rates. Many SNP-poor regions were substantially longer than most SNP-rich regions, covering up to 4 Mb, and possibly reflecting introgression between the respective gene pools that may have occurred hundreds of years ago. Although 46.2% +/- 8.3% of the SNPs differentiate other pairs of japonica and indica genotypes, SNP rates in rice were not predictive of evolutionary rates for corresponding genes in another grass species, sorghum. The data set is freely available at http://www.plantgenome.uga.edu/snp.

Microsatellite identification and characterization in peanut ( A. hypogaea L.)

A major constraint to the application of biotechnology to the improvement of the allotetraploid peanut, or groundnut ( Arachis hypogaea L.), has been the paucity of polymorphism among germplasm lines using biochemical (seed proteins, isozymes) and DNA markers (RFLPs and RAPDs). Six sequence-tagged microsatellite (STMS) markers were previously available that revealed polymorphism in cultivated peanut. Here, we identify and characterize 110 STMS markers that reveal genetic variation in a diverse array of 24 peanut landraces. The simple-sequence repeats (SSRs) were identified with a probe of two 27648-clone genomic libraries: one constructed using PstI and the other using Sau3AI/ BamHI. The most frequent, repeat motifs identified were ATT and GA, which represented 29% and 28%, respectively, of all SSRs identified. These were followed by AT, CTT, and GT. Of the amplifiable primers, 81% of ATT and 70.8% of GA repeats were polymorphic in the cultivated peanut test array. The repeat motif AT showed the maximum number of alleles per locus (5.7). Motifs ATT, GT, and GA had a mean number of alleles per locus of 4.8, 3.8, and 3.6, respectively. The high mean number of alleles per polymorphic locus, combined with their relative frequency in the genome and amenability to probing, make ATT and GA the most useful and appropriate motifs to target to generate further SSR markers for peanut.

An EST survey of the sugarcane transcriptome

Its large genome and high polyploidy makes sugarcane (Saccharum spp.) a singularly challenging crop to study and improve using genetic approaches. To provide large numbers of functionally characterized candidate genes that might be tested for direct association (rather than distant linkage) with economically important traits, we sequenced the 5' ends of 9,216 clones from three cDNA libraries (apex, leaf and mature internode), representing 3,401 non-redundant sequences. About 57% of these sequences could be assigned a tentative function based on statistically significant similarity to previously characterized proteins or DNA sequences. Another 28% corresponded to previously identified, but uncharacterized, sequences. Some of the remaining unidentified sequences were predicted to be genes which could potentially be new to plants or unique to sugarcane. Comparisons of the sugarcane ESTs to a large sorghum EST database revealed similar compositions of expressed genes between some different tissues. Comparison to a detailed Arabidopsis protein database showed some highly conserved sequences, which might be useful DNA markers for pan-angiosperm comparative mapping. These EST sequences provide a foundation for many new studies to accelerate isolation of agronomically important genes from the cumbersome sugarcane genome.

A rapid method for manual or automated purification of fluorescently labeled nucleic acids for sequencing, genotyping, and microarrays

Fluorescent dyes provide specific, sensitive, and multiplexed detection of nucleic acids. To maximize sensitivity, fluorescently labeled reaction products (e.g., cycle sequencing or primer extension products) must be purified away from residual dye-labeled precursors. Successful high-throughput analyses require that this purification be reliable, rapid, and amenable to automation. Common methods for purifying reaction products involve several steps and require processes that are not easily automated. Prolinx, Inc. has devel oped RapXtract superparamagnetic separation technology affording rapid and easy-to-perform methods that yield high-quality product and are easily automated. The technology uses superparamagnetic particles that specifically remove unincorporated dye-labeled precursors. These particles are efficiently pelleted in the presence of a magnetic field, making them ideal for purification because of the rapid separations that they allow. RapXtract-purified sequencing reactions yield data with good signal and high Phred quality scores, and they work with various sequencing dye chemistries, including BigDye and near-infrared fluorescence IRDyes. RapXtract technology can also be used to purify dye primer sequencing reactions, primer extension reactions for genotyping analysis, and nucleic acid labeling reactions for microarray hybridization. The ease of use and versatility of RapXtract technology makes it a good choice for manual or automated purification of fluorescently labeled nucleic acids.

Integration of Cot analysis, DNA cloning, and high-throughput sequencing facilitates genome characterization and gene discovery

Cot-based sequence discovery represents a powerful means by which both low-copy and repetitive sequences can be selectively and efficiently fractionated, cloned, and characterized. Based upon the results of a Cot analysis, hydroxyapatite chromatography was used to fractionate sorghum (Sorghum bicolor) genomic DNA into highly repetitive (HR), moderately repetitive (MR), and single/low-copy (SL) sequence components that were consequently cloned to produce HRCot, MRCot, and SLCot genomic libraries. Filter hybridization (blotting) and sequence analysis both show that the HRCot library is enriched in sequences traditionally found in high-copy number (e.g., retroelements, rDNA, centromeric repeats), the SLCot library is enriched in low-copy sequences (e.g., genes and "nonrepetitive ESTs"), and the MRCot library contains sequences of moderate redundancy. The Cot analysis suggests that the sorghum genome is approximately 700 Mb (in agreement with previous estimates) and that HR, MR, and SL components comprise 15%, 41%, and 24% of sorghum DNA, respectively. Unlike previously described techniques to sequence the low-copy components of genomes, sequencing of Cot components is independent of expression and methylation patterns that vary widely among DNA elements, developmental stages, and taxa. High-throughput sequencing of Cot clones may be a means of "capturing" the sequence complexity of eukaryotic genomes at unprecedented efficiency.

Development of multichannel devices with an array of electrospray tips for high-throughput mass spectrometry

The basic principles of multichannel devices with an array of electrospray tips for high-throughput infusion electrospray ionization mass spectrometry (ESI-MS) have been developed. The prototype plastic devices were fabricated by casting from a solvent-resistant resin. The sample wells on the device were arranged in the format of the standard 96-microtiter well plate, with each sample well connected to an independent electrospray exit port via a microchannel with imbedded electrode. A second plastic plate with distribution microchannels was employed as a cover plate and pressure distributor. Nitrogen gas was used to pressurize individual wells for transport of sample into the electrospray exit port. The design of independent microchannels and electrospray exit ports allowed very high throughput and duty cycle, as well as elimination of any potential sample carryover. The device was placed on a computer-controlled translation stage for precise positioning of the electrospray exit ports in front of the mass spectrometer sampling orifice. High-throughput ESI-MS was demonstrated by analyzing 96 peptide samples in 480 s, corresponding to a potential throughput of 720 samples/h. As a model application, the device was used for the MS determination of inhibition constants of several inhibitors of HIV-1 protease.

High-throughput bioanalytical LC/MS/MS determination of benzodiazepines in human urine: 1000 samples per 12 hours

The analytical capabilities of liquid chromatography tandem mass spectrometry for sensitive and highly selective determination of target compounds in complex biological samples makes it well suited for high-throughput analysis. We report the fast separation of six benzodiazepines isolated from human urine via selected reaction monitoring liquid chromatography/mass spectrometry using short dwell times to accommodate fast-eluting chromatographic peaks. The analytes were extracted from human urine samples along with their deuterium-labeled internal standards by a simple liquid-liquid extraction in 96-well plates. Using four autosamplers coupled to one chromatographic column and one tandem mass spectrometer operated in the turbo ion spray mode with positive ion detection, 1152 samples (12 96-well plates) were analyzed in less than 12 h. Through an electronic switching box designed and constructed in-house, the autosamplers were synchronized with the mass spectrometer so that injections were made as soon as the mass spectrometer was ready to collect data. Each run required 30 s to complete with another 7-8 s for the data system to load the next data file to be collected. Chromatographic integrity and ion current response remained relatively constant for the duration of the analyses. The results show acceptable precision and accuracy and demonstrate the feasibility of using fast separations with tandem mass spectrometry for high-throughout analysis of biological samples containing multiple analytes.