Adam English, lead bioinformatics programmer at Baylor College of Medicine, discusses challenges with resolving gaps in high-quality draft genome assemblies. Sequencing biases, repetitive genomic features, genomic polymorphism, and other complicating factors all come together to make some regions difficult or impossible to assemble. For more facile assembly and automated finishing of draft genomes, he presents an automated approach to finishing using long reads from the PacBio System. The tool PBJelly automates the finishing process using long sequence reads in a reference-guided assembly process. Using PBJelly and SMRT Sequencing, they upgraded the draft genome sequences of a simulated Drosophila melanogaster, the version…
Completing a genome is an important goal of genome assembly. However, many assemblies, including reference assemblies, are unfinished and have a number of gaps. Long reads obtained from third-generation sequencing (TGS) platforms can help close these gaps and improve assembly contiguity. However, current gap-closure approaches using long reads require extensive runtime and high memory usage. Thus, a fast and memory-efficient approach using long reads is needed to obtain complete genomes.We developed LR_Gapcloser to rapidly and efficiently close the gaps in genome assembly. This tool utilizes long reads generated from TGS sequencing platforms. Tested on de novo assembled gaps, repeat-derived gaps,…
In addition to the BAC-based reference sequence of the accession Columbia-0 from the year 2000, several short read assemblies of THE plant model organism Arabidopsis thaliana were published during the last years. Also, a SMRT-based assembly of Landsberg erecta has been generated that identified translocation and inversion polymorphisms between two genotypes of the species. Here we provide a chromosome-arm level assembly of the A. thaliana accession Niederzenz-1 (AthNd-1_v2c) based on SMRT sequencing data. The best assembly comprises 69 nucleome sequences and displays a contig length of up to 16 Mbp. Compared to an earlier Illumina short read-based NGS assembly (AthNd-1_v1),…
Contaminant sequences that appear in published genomes can cause numerous problems for downstream analyses, particularly for evolutionary studies and metagenomics projects. Our large-scale scan of complete and draft bacterial and archaeal genomes in the NCBI RefSeq database reveals that 2250 genomes are contaminated by human sequence. The contaminant sequences derive primarily from high-copy human repeat regions, which themselves are not adequately represented in the current human reference genome, GRCh38. The absence of the sequences from the human assembly offers a likely explanation for their presence in bacterial assemblies. In some cases, the contaminating contigs have been erroneously annotated as containing…
Construction of chromosome-level assembly is a vital step in achieving the goal of a ‘Platinum’ genome, but it remains a major challenge to assemble and anchor sequences to chromosomes in autopolyploid or highly heterozygous genomes. High-throughput chromosome conformation capture (Hi-C) technology serves as a robust tool to dramatically advance chromosome scaffolding; however, existing approaches are mostly designed for diploid genomes and often with the aim of reconstructing a haploid representation, thereby having limited power to reconstruct chromosomes for autopolyploid genomes. We developed a novel algorithm (ALLHiC) that is capable of building allele-aware, chromosomal-scale assembly for autopolyploid genomes using Hi-C paired-end…
Wild almond species accumulate the bitter and toxic cyanogenic diglucoside amygdalin. Almond domestication was enabled by the selection of genotypes harboring sweet kernels. We report the completion of the almond reference genome. Map-based cloning using an F1 population segregating for kernel taste led to the identification of a 46-kilobase gene cluster encoding five basic helix-loop-helix transcription factors, bHLH1 to bHLH5. Functional characterization demonstrated that bHLH2 controls transcription of the P450 monooxygenase-encoding genes PdCYP79D16 and PdCYP71AN24, which are involved in the amygdalin biosynthetic pathway. A nonsynonymous point mutation (Leu to Phe) in the dimerization domain of bHLH2 prevents transcription of the…
The advent of Nanopore sequencing has realised portable genomic research and applications. However, state of the art long read aligners and large reference genomes are not compatible with most mobile computing devices due to their high memory requirements. We show how memory requirements can be reduced through parameter optimisation and reference genome partitioning, but highlight the associated limitations and caveats of these approaches. We then demonstrate how these issues can be overcome through an appropriate merging technique. We incorporated multi-index merging into the Minimap2 aligner and demonstrate that long read alignment to the human genome can be performed on a…
The killer immunoglobulin-like receptors (KIR) genes belong to the immunoglobulin superfamily and are widely studied due to the critical role they play in coordinating the innate immune response to infection and disease. Highly accurate, contiguous, long reads, like those generated by SMRT Sequencing, when combined with target-enrichment protocols, provide a straightforward strategy for generating complete de novo assembled KIR haplotypes. We have explored two different methods to capture the KIR region; one applying the use of fosmid clones and one using Nimblegen capture.