Genome size evolution in the beetle genus Diabrotica

Diabrocite corn rootworms are one of the most economically significant pests of maize in the United States and Europe and an emerging model for insect-plant interactions. Genome sizes of several species in the genus Diabrotica were estimated using flow cytometry along with that of Acalymma vittatum as an outgroup. Within the Diabrotica subgroups fucata and virgifera, genome sizes ranged between 1.59 - 1.68 gigabase pairs (Gb) and between 2.31- 2.65 Gb, respectively, and the Acalymma vittatum genome size was around 1.69 Gb. This result indicated that a substantial increase in genome size occurred in the ancestor of the virgifera group. Further analysis of fucata group and virgifera group genome sequencing reads indicated that the genome size difference between the Diabrotica subgroups could be attributed to a higher content of transposable elements, mostly miniature inverted-transposable elements (MITEs) and LTR gypsy-like elements.

Benchmarking transposable element annotation methods for creation of a streamlined, comprehensive pipeline

Background Sequencing technology and assembly algorithms have matured to the point that high-quality de novo assembly is possible for large, repetitive genomes. Current assemblies traverse transposable elements (TEs) and provide an opportunity for comprehensive annotation of TEs. Numerous methods exist for annotation of each class of TEs, but their relative performances have not been systematically compared. Moreover, a comprehensive pipeline is needed to produce a non-redundant library of TEs for species lacking this resource to generate whole-genome TE annotations. Results We benchmark existing programs based on a carefully curated library of rice TEs. We evaluate the performance of methods annotating long terminal repeat (LTR) retrotransposons, terminal inverted repeat (TIR) transposons, short TIR transposons known as miniature inverted transposable elements (MITEs), and Helitrons. Performance metrics include sensitivity, specificity, accuracy, precision, FDR, and F1. Using the most robust programs, we create a comprehensive pipeline called Extensive de-novo TE Annotator (EDTA) that produces a filtered non-redundant TE library for annotation of structurally intact and fragmented elements. EDTA also deconvolutes nested TE insertions frequently found in highly repetitive genomic regions. Using other model species with curated TE libraries (maize and Drosophila), EDTA is shown to be robust across both plant and animal species. Conclusions The benchmarking results and pipeline developed here will greatly facilitate TE annotation in eukaryotic genomes. These annotations will promote a much more in-depth understanding of the diversity and evolution of TEs at both intra- and inter-species levels. EDTA is open-source and freely available: https://github.com/oushujun/EDTA.

Truncated Non-Nuclear Transposable Elements in Grapevine: A Mini Review

In this mini-review we present insight to the non-nuclear transposable elements and in silico analysis of miniature inverted transposable elements (MITEs) in the grapevine mitochondrial genome. Here we report the identification of 17 truncated sequences in grapevine (Vitis vinifera L.) mitochondrial genome which expectedly belongs to the four ancient transposon families (hAT, Tc1Mariner, Mutator and PIF/Harbinger). Some sequences with a high rate of homology in chloroplast and nuclear genomes were also identified. Thus, it suggests the intercellular gene transfer between these three organelles. These partial sequences showed a high level of similitude with full MITE sequences, and they were found in their inner region, supporting their MITE origin. Further analysis revealed these sequences in other life kingdoms (including eubacteria and archaea), which indicates their ancient origin. Further research showed that 13 out of the 17 sequences are conserved domains of the genes where they are located, suggesting their contribution to gene evolution. Therefore, we suppose that more studies of nature, origin and functional meaning of these sequences and their fusion with genes are necessary. In the light of our observations it will be useful for further studies of V. vinifera genome organizing and systematics, as well as for other species.

Comparison of orthologous and paralogous DNA flanking the wheat high molecular weight glutenin genes: sequence conservation and divergence, transposon distribution, and matrix-attachment regions

Extended flanking DNA sequences were characterized for five members of the wheat high molecular weight (HMW) glutenin gene family to understand more of the structure, control, and evolution of these genes. Analysis revealed more sequence conservation among orthologous regions than between paralogous regions, with differences mainly owing to transposition events involving putative retrotransposons and several miniature inverted transposable elements (MITEs). Both gyspy-like long terminal repeat (LTR) and non-LTR retrotransposon sequences are represented in the flanking DNAs. One of the MITEs is a novel class, but another MITE is related to the maize Stowaway family and is widely represented in Triticeae express sequence tags (ESTs). Flanking DNA of the longest sequence, a 20 425-bp fragment including and surrounding the HMW-glutenin Bx7 gene, showed additional cereal gene-like sequences both immediately 5' and 3' to the HMW-glutenin coding region. The transcriptional activities of sequences related to these flanking putative genes and the retrotransposon-related regions were indicated by matches to wheat and other Triticeae ESTs. Predictive analysis of matrix-attachment regions (MARs) of the HMW glutenin and several α-, γ-, and ω-gliadin flanking DNAs indicate potential MARs immediately flanking each of the genes. Matrix binding activity in the predicted regions was confirmed for two of the HMW-glutenin genes.Key words: wheat, glutenins, evolution, matrix-attachment regions, transposable elements.