The nature of intraspecific genome size variation in taxonomically complex eyebrights

SummaryGenome size (GS) is a key trait related to morphology, life history, and evolvability. Although GS is, by definition, affected by presence/absence variants (PAVs), which are ubiquitous in population sequencing studies, GS is often treated as an intrinsic property of a species. Here, we studied intra- and interspecific GS variation in taxonomically complex British eyebrights (Euphrasia).We generated GS data for 192 individuals of diploid and tetraploid Euphrasia and analysed GS variation in relation to ploidy, taxonomy, population affiliation, and geography. We further compared the genomic repeat content of 30 samples.We found considerable genuine intraspecific GS variation, and observed isolation-by-distance for GS in outcrossing diploids. Tetraploid Euphrasia showed contrasting patterns, with GS increasing with latitude in outcrossing Euphrasia arctica, but little GS variation in the highly selfing Euphrasia micrantha. Interspecific differences in GS genomic repeat percentages were small.We show the utility of treating GS as the outcome of polygenic variation. Like other types of genetic variation, such as single nucleotide polymorphisms, GS variation may be increased through hybridisation and population subdivision. In addition to selection on associated traits, GS is predicted to be affected indirectly by selection due to pleiotropy of the underlying PAVs.

Genomic Repeat Element Analyzer for Mammals (GREAM)

Background: Understanding the mechanism behind the transcriptional regulation of genes is still a challenge. Recent findings indicate that the genomic repeat elements (such as LINES, SINES and LTRs) could play an important role in the transcription control. Hence, it is important to further explore the role of genomic repeat elements in the gene expression regulation, and perhaps in other molecular processes. Although many computational tools exists for repeat element analysis, almost all of them simply identify and/or classifying the genomic repeat elements within query sequence(s); none of them facilitate identification of repeat elements that are likely to have a functional significance, particularly in the context of transcriptional regulation. Result: We developed the 'Genomic Repeat Element Analyzer for Mammals' (GREAM) to allow gene-centric analysis of genomic repeat elements in 17 mammalian species, and validated it by comparing with some of the existing experimental data. The output provides a categorized list of the specific type of transposons, retro-transposons and other genome-wide repeat elements that are statistically over-represented across specific neighborhood regions of query genes. The position and frequency of these elements, within the specified regions, are displayed as well. The tool also offers queries for position-specific distribution of repeat elements within chromosomes. In addition, GREAM facilitates the analysis of repeat element distribution across the neighborhood of orthologous genes. Conclusion: GREAM allows researchers to short-list the potentially important repeat elements, from the genomic neighborhood of genes, for further experimental analysis. GREAM is free and available for all at http://resource.ibab.ac.in/GREAM/