In recent years, human genomic research has focused on comparing short-read data sets to a single human reference genome. However, it is becoming increasingly clear that significant structural variations present in individual human genomes are missed or ignored by this approach. Additionally, remapping short-read data limits the phasing of variation among individual chromosomes. This reduces the newly sequenced genome to a table of single nucleotide polymorphisms (SNPs) with little to no information as to the co-linearity (phasing) of these variants, resulting in a “mosaic” reference representing neither of the parental chromosomes. The variation between the homologous chromosomes is lost in…
Each human genome has thousands of structural variants compared to the reference assembly, up to 85% of which are difficult or impossible to detect with Illumina short reads and are only visible with long, multi-kilobase reads. The PacBio RS II and Sequel single molecule, real-time (SMRT) sequencing platforms have made it practical to generate long reads at high throughput. These platforms enable the discovery of structural variants just as short-read platforms did for single nucleotide variants. Numerous software algorithms call structural variants effectively from PacBio long reads, but algorithm sensitivity is lower for insertion variants and all heterozygous variants. Furthermore,…
Until recently only two genome assemblies were publicly available for grapevine—both Vitis vinifera L. Cv. Pinot Noir (PN). The best available PN genome assembly (Jaillon et al. 2007) is not representative of the genome complexity that is typical of wine-grape cultivars in the field and it is highly fragmented. To assess the genetic complexities of Chardonnay grapevine, assembly of a new de novo reference genome was needed. Here we describe a draft assembly using PacBio SMRT Sequencing data and PacBio’s new phased diploid genome assembler FALCON-Unzip (Chin et al. 2016).
While genome assembly projects have been successful in many haploid and inbred species, the assembly of non-inbred or rearranged heterozygous genomes remains a major challenge. To address this challenge, we introduce the open-source FALCON and FALCON-Unzip algorithms (https://github.com/PacificBiosciences/FALCON/) to assemble long-read sequencing data into highly accurate, contiguous, and correctly phased diploid genomes. We generate new reference sequences for heterozygous samples including an F1 hybrid of Arabidopsis thaliana, the widely cultivated Vitis vinifera cv. Cabernet Sauvignon, and the coral fungus Clavicorona pyxidata, samples that have challenged short-read assembly approaches. The FALCON-based assemblies are substantially more contiguous and complete than alternate short-…
Aedes aegypti is a tropical and subtropical mosquito vector for Zika, yellow fever, dengue fever, chikungunya, and other diseases. The outbreak of Zika in the Americas, which can cause microcephaly in the fetus of infected women, adds urgency to the need for a high-quality reference genome in order to better understand the organism’s biology and its role in transmitting human disease. We describe the first diploid assembly of an insect genome, using SMRT sequencing and the open-source assembler FALCON-Unzip. This assembly has high contiguity (contig N50 1.3 Mb), is more complete than previous assemblies (Length 1.45 Gb with 87% BUSCO…
Many applications of high throughput sequencing rely on the availability of an accurate reference genome. Errors in the reference genome assembly increase the number of false-positives in downstream analyses. Recently, we have shown that over 33% of the current pig reference genome, Sscrofa10.2, is either misassembled or otherwise unreliable for genomic analyses. Additionally, ~10% of the bases in the assembly are Ns in gaps of an arbitrary size. Thousands of highly fragmented contigs remain unplaced and many genes are known to be missing from the assembly. Here we present a new assembly of the pig genome, Sscrofa11, assembled using 65X…
Bipolar disorder (BD) is a phenotypically and genetically complex and debilitating neurological disorder that affects 1% of the worldwide population. There is compelling evidence from family, twin and adoption studies supporting the involvement of a genetic predisposition in BD with estimated heritability up to ~ 80%. The risk in first-degree relatives is ten times higher than in the general population. Linkage and association studies have implicated multiple putative chromosomal loci for BP susceptibility, however no disease genes have been identified to date.
To test the impact of high-quality genome assemblies on biological research, we applied PacBio long-read sequencing in conjunction with the new, diploid-aware FALCON-Unzip assembler to a number of bird species. These included: the zebra finch, for which a consortium-generated, Sanger-based reference exists, to determine how the FALCON-Unzip assembly would compare to the current best references available; Anna’s hummingbird genome, which had been assembled with short-read sequencing methods as part of the Avian Phylogenomics phase I initiative; and two critically endangered bird species (kakapo and ‘alala) of high importance for conservations efforts, whose genomes had not previously been sequenced and assembled.
Aedes aegypti is a tropical and subtropical mosquito vector for Zika, yellow fever, dengue fever, and chikungunya. We describe the first diploid assembly of an insect genome, using SMRT Sequencing and the open-source assembler FALCON-Unzip. This assembly has high contiguity (contig N50 1.3 Mb), is more complete than previous assemblies (Length 1.45 Gb with 87% BUSCO genes complete), and is high quality (mean base >QV30 after polishing). Long-range haplotype structure, in some cases encompassing more than 4 Mb of extremely divergent homologous sequence with dramatic differences in coding sequence content, is resolved using a combination of the FALCON-Unzip assembler, genome…
Despite amazing progress over the past quarter century in the technology to detect genetic variants, intermediate-sized structural variants (50 bp to 50 kb) have remained difficult to identify. Such variants are too small to detect with array comparative genomic hybridization, but too large to reliably discover with short-read DNA sequencing. Recent de novo assemblies of human genomes have demonstrated the power of PacBio Single Molecule, Real-Time (SMRT) Sequencing to fill this technology gap and sensitively identify structural variants in the human genome. While de novo assembly is the ideal method to identify variants in a genome, it requires high depth…
Though a role for structural variants in human disease has long been recognized, it has remained difficult to identify intermediate-sized variants (50 bp to 5 kb), which are too small to detect with array comparative genomic hybridization, but too large to reliably discover with short-read DNA sequencing. Recent studies have demonstrated that PacBio Single Molecule, Real-Time (SMRT) sequencing fills this technology gap. SMRT sequencing detects tens of thousands of structural variants in the human genome, approximately five times the sensitivity of short-read DNA sequencing.
De novo assembly is a large part of JGI’s analysis portfolio. Repetitive DNA sequences are abundant in a wide range of organisms we sequence and pose a significant technical challenge for assembly. We are interested in long read technologies capable of spanning genomic repeats to produce better assemblies. We currently have three RS II and two Sequel PacBio machines. RS II machines are primarily used for fungal and microbial genome assembly as well as synthetic biology validation. Between microbes and fungi we produce hundreds of PacBio libraries a year and for throughput reasons the vast majority of these are >10…
A single gene may encode a surprising number of proteins, each with a distinct biological function. This is especially true in complex eukaryotes. Short- read RNA sequencing (RNA-seq) works by physically shearing transcript isoforms into smaller pieces and bioinformatically reassembling them, leaving opportunity for misassembly or incomplete capture of the full diversity of isoforms from genes of interest. The PacBio Isoform Sequencing (Iso-Seq™) method employs long reads to sequence transcript isoforms from the 5’ end to their poly-A tails, eliminating the need for transcript reconstruction and inference. These long reads result in complete, unambiguous information about alternatively spliced exons, transcriptional…
A high quality reference genome is an essential resource for plant and animal breeding and functional and evolutionary studies. The common hop (Humulus lupulus, Cannabaceae) is an economically important crop plant used to flavor and preserve beer. Its genome is large (flow cytometrybased estimates of diploid length >5.4Gb1), highly repetitive, and individual plants display high levels of heterozygosity, which make assembly of an accurate and contiguous reference genome challenging with conventional short-read methods. We present a contig assembly of Cascade Hops using PacBio long reads and the diploid genome assembler, FALCON-Unzip2. The assembly has dramatically improved contiguity and completeness over…
The Pacific Biosciences Iso-Seq method, which can produce high-quality isoform sequences of 10 kb and longer, has been used to annotate many important plant and animal genomes. Here, we develop an algorithm called IsoPhase that postprocesses Iso-Seq data to retrieve allele specific isoform information. Using simulated data, we show that for both diploid and tetraploid genomes, IsoPhase results in good SNP recovery with low FDR at error rates consistent with CCS reads. We apply IsoPhase to a haplotyperesolved genome assembly and multiple fetal tissue Iso-Seq dataset from a F1 cross of Angus x Brahman cattle subspecies. IsoPhase-called haplotypes were validated…