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July 1, 2018

Hotspots of independent and multiple rounds of LTR-retrotransposon bursts in Brassica species

Long terminal repeat retrotransposons (LTR-RTs) are a predominant group of plant transposable elements (TEs) that are an important component of plant genomes. A large number of LTR-RTs have been annotated in the genomes of the agronomically important oil and vegetable crops of the genus Brassica. Herein, full-length LTR-RTs in the genomes of Brassica and other closely related species were systematically analyzed. The full-length LTR-RT content varied greatly (from 0.43% to 23.4%) between different species, with Gypsy-like LTR-RTs constituting a primary group across these genomes. More importantly, many annotated LTR-RTs (from 10.03% to 33.25% of all detected LTR-RTs) were found to…

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February 15, 2018

Structure and distribution of centromeric retrotransposons at diploid and allotetraploid Coffea centromeric and pericentromeric regions.

Centromeric regions of plants are generally composed of large array of satellites from a specific lineage ofGypsyLTR-retrotransposons, called Centromeric Retrotransposons. Repeated sequences interact with a specific H3 histone, playing a crucial function on kinetochore formation. To study the structure and composition of centromeric regions in the genusCoffea, we annotated and classified Centromeric Retrotransposons sequences from the allotetraploidC. arabicagenome and its two diploid ancestors:Coffea canephoraandC. eugenioides. Ten distinct CRC (Centromeric Retrotransposons inCoffea) families were found. The sequence mapping and FISH experiments of CRC Reverse Transcriptase domains inC. canephora, C. eugenioides, andC. arabicaclearly indicate a strong and specific targeting mainly onto proximal…

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February 1, 2018

LTR_retriever: A highly accurate and sensitive program for identification of long terminal repeat retrotransposons.

Long terminal repeat retrotransposons (LTR-RTs) are prevalent in plant genomes. The identification of LTR-RTs is critical for achieving high-quality gene annotation. Based on the well-conserved structure, multiple programs were developed for the de novo identification of LTR-RTs; however, these programs are associated with low specificity and high false discovery rates. Here, we report LTR_retriever, a multithreading-empowered Perl program that identifies LTR-RTs and generates high-quality LTR libraries from genomic sequences. LTR_retriever demonstrated significant improvements by achieving high levels of sensitivity (91%), specificity (97%), accuracy (96%), and precision (90%) in rice (Oryza sativa). LTR_retriever is also compatible with long sequencing reads. With…

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November 6, 2017

PacBio sequencing reveals transposable element as a key contributor to genomic plasticity and virulence variation in Magnaporthe oryzae.

The sustainable cultivation of rice, which serves as staple food crop for more than half of the world's population, is under serious threat due to the huge yield losses inflicted by rice blast disease caused by the globally destructive fungus Magnaporthe oryzae (Pyricularia oryzae) (Dean et al., 2012, Nalley et al., 2016, Deng et al., 2017). This filamentous ascomycete fungus is also capable of causing blast infection on other economically important cereal crops, including wheat, millet, and barley, making it the world's most important plant pathogenic fungus (Zhong et al., 2016). The advent of whole-genome sequencing technology and the subsequent…

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August 7, 2017

Retrotransposons are the major contributors to the expansion of the Drosophila ananassae Muller F element.

The discordance between genome size and the complexity of eukaryotes can partly be attributed to differences in repeat density. The Muller F element (~5.2 Mb) is the smallest chromosome in Drosophila melanogaster, but it is substantially larger (>18.7 Mb) in D. ananassae To identify the major contributors to the expansion of the F element and to assess their impact, we improved the genome sequence and annotated the genes in a 1.4-Mb region of the D. ananassae F element, and a 1.7-Mb region from the D element for comparison. We find that transposons (particularly LTR and LINE retrotransposons) are major contributors…

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August 1, 2017

Comparative genomics of two sequential Candida glabrata clinical isolates.

Candida glabrata is an important fungal pathogen which develops rapid antifungal resistance in treated patients. It is known that azole treatments lead to antifungal resistance in this fungal species and that multidrug efflux transporters are involved in this process. Specific mutations in the transcriptional regulator PDR1 result in upregulation of the transporters. In addition, we showed that the PDR1 mutations can contribute to enhance virulence in animal models. In this study, we were interested to compare genomes of two specific C. glabrata-related isolates, one of which was azole susceptible (DSY562) while the other was azole resistant (DSY565). DSY565 contained a…

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March 17, 2017

A comprehensive approach to expression of L1 loci.

L1 elements represent the only currently active, autonomous retrotransposon in the human genome, and they make major contributions to human genetic instability. The vast majority of the 500 000 L1 elements in the genome are defective, and only a relatively few can contribute to the retrotransposition process. However, there is currently no comprehensive approach to identify the specific loci that are actively transcribed separate from the excess of L1-related sequences that are co-transcribed within genes. We have developed RNA-Seq procedures, as well as a 1200 bp 5? RACE product coupled with PACBio sequencing that can identify the specific L1 loci…

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July 1, 2016

Analysis of tandem gene copies in maize chromosomal regions reconstructed from long sequence reads.

Haplotype variation not only involves SNPs but also insertions and deletions, in particular gene copy number variations. However, comparisons of individual genomes have been difficult because traditional sequencing methods give too short reads to unambiguously reconstruct chromosomal regions containing repetitive DNA sequences. An example of such a case is the protein gene family in maize that acts as a sink for reduced nitrogen in the seed. Previously, 41-48 gene copies of the alpha zein gene family that spread over six loci spanning between 30- and 500-kb chromosomal regions have been described in two Iowa Stiff Stalk (SS) inbreds. Analyses of…

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June 14, 2016

Genome-wide characterization of human L1 antisense promoter-driven transcripts.

Long INterspersed Element-1 (LINE-1 or L1) is the only autonomously active, transposable element in the human genome. L1 sequences comprise approximately 17 % of the human genome, but only the evolutionarily recent, human-specific subfamily is retrotransposition competent. The L1 promoter has a bidirectional orientation containing a sense promoter that drives the transcription of two proteins required for retrotransposition and an antisense promoter. The L1 antisense promoter can drive transcription of chimeric transcripts: 5' L1 antisense sequences spliced to the exons of neighboring genes.The impact of L1 antisense promoter activity on cellular transcriptomes is poorly understood. To investigate this, we analyzed GenBank…

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June 1, 2016

A hot L1 retrotransposon evades somatic repression and initiates human colorectal cancer.

Although human LINE-1 (L1) elements are actively mobilized in many cancers, a role for somatic L1 retrotransposition in tumor initiation has not been conclusively demonstrated. Here, we identify a novel somatic L1 insertion in the APC tumor suppressor gene that provided us with a unique opportunity to determine whether such insertions can actually initiate colorectal cancer (CRC), and if so, how this might occur. Our data support a model whereby a hot L1 source element on Chromosome 17 of the patient's genome evaded somatic repression in normal colon tissues and thereby initiated CRC by mutating the APC gene. This insertion…

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May 10, 2016

Next-generation sequencing-based detection of germline L1-mediated transductions.

While active LINE-1 (L1) elements possess the ability to mobilize flanking sequences to different genomic loci through a process termed transduction influencing genomic content and structure, an approach for detecting polymorphic germline non-reference transductions in massively-parallel sequencing data has been lacking.Here we present the computational approach TIGER (Transduction Inference in GERmline genomes), enabling the discovery of non-reference L1-mediated transductions by combining L1 discovery with detection of unique insertion sequences and detailed characterization of insertion sites. We employed TIGER to characterize polymorphic transductions in fifteen genomes from non-human primate species (chimpanzee, orangutan and rhesus macaque), as well as in a human…

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April 12, 2016

Radical remodeling of the Y chromosome in a recent radiation of malaria mosquitoes.

Y chromosomes control essential male functions in many species, including sex determination and fertility. However, because of obstacles posed by repeat-rich heterochromatin, knowledge of Y chromosome sequences is limited to a handful of model organisms, constraining our understanding of Y biology across the tree of life. Here, we leverage long single-molecule sequencing to determine the content and structure of the nonrecombining Y chromosome of the primary African malaria mosquito, Anopheles gambiae. We find that the An. gambiae Y consists almost entirely of a few massively amplified, tandemly arrayed repeats, some of which can recombine with similar repeats on the X…

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April 1, 2016

Long-read sequence assembly of the gorilla genome.

Accurate sequence and assembly of genomes is a critical first step for studies of genetic variation. We generated a high-quality assembly of the gorilla genome using single-molecule, real-time sequence technology and a string graph de novo assembly algorithm. The new assembly improves contiguity by two to three orders of magnitude with respect to previously released assemblies, recovering 87% of missing reference exons and incomplete gene models. Although regions of large, high-identity segmental duplications remain largely unresolved, this comprehensive assembly provides new biological insight into genetic diversity, structural variation, gene loss, and representation of repeat structures within the gorilla genome. The…

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March 23, 2016

High quality maize centromere 10 sequence reveals evidence of frequent recombination events.

The ancestral centromeres of maize contain long stretches of the tandemly arranged CentC repeat. The abundance of tandem DNA repeats and centromeric retrotransposons (CR) has presented a significant challenge to completely assembling centromeres using traditional sequencing methods. Here, we report a nearly complete assembly of the 1.85 Mb maize centromere 10 from inbred B73 using PacBio technology and BACs from the reference genome project. The error rates estimated from overlapping BAC sequences are 7 × 10(-6) and 5 × 10(-5) for mismatches and indels, respectively. The number of gaps in the region covered by the reassembly was reduced from 140…

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February 12, 2016

AGBT Conference: Long-read sequence of the gorilla genome

Christopher Hill presents data from efforts to produce reference-grade assemblies for the great ape species. Using SMRT Sequencing, Hill and his colleagues are generating assemblies with much higher contiguity to resolve repetitive and other particularly complex regions. In this talk, he focuses on data from their new high-quality gorilla assembly.

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