Alexandros Bousios
Profile Url: alexandros-bousios
Researcher at University of Sussex
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Video Abstract (AI generated)
Paper
Preprint
Plant transposable elements (TEs) regularly capture fragments of genes. When the host silences these TEs, siRNAs homologous to the captured regions may also target the genes. This epigenetic cross-talk establishes an intragenomic conflict: silencing the TEs has the cost of silencing the genes. If genes are important, however, natural selection may maintain function by moderating the silencing response, which may also advantage the TEs. Here, we examined this model by focusing on three TE families in maize: Helitrons, Pack-MULEs and Sirevirus LTR retrotransposons. We documented 1,263 TEs containing exon fragments from 1,629 donor genes. Consistent with epigenetic conflict, donor genes mapped more siRNAs and were more methylated than genes with no evidence of capture. However, these patterns differed between syntelog vs. translocated donor genes. Syntelogs appeared to maintain function, as measured by gene expression, consistent with moderation of silencing for functionally important genes. Epigenetic marks did not spread beyond their captured regions and 24nt cross-talk siRNAs were linked with CHH methylation. Translocated genes, in contrast, bore the signature of silencing by being highly methylated and less expressed. They were also overrepresented among donor genes, suggesting a link between capture and gene movement. The evidence for an advantage to TEs was less obvious. TEs with captured fragments were older, mapped fewer siRNAs and were slightly less methylated than TEs without captured fragments but showed no evidence of increased copy numbers. Altogether, our results demonstrate that TE capture triggers an epigenetic conflict for important genes, but it may lead to pseudogenization for less constrained genes. ### Competing Interest Statement The authors have declared no competing interest.
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BMC Psychology, 2017-02-15
Video Abstract (AI generated)
Paper
Preprint
BMC Psychology
The advent of high-throughput sequencing (HTS) has revolutionized the way in which epigenetic research is conducted. Often coupled with the availability of fully sequenced genomes, millions of small RNA (sRNA) reads are mapped to regions of interest and the results scrutinized for clues about epigenetic mechanisms. However, this approach requires careful consideration in regards to experimental design, especially when one investigates repetitive parts of genomes such as transposable elements (TEs), and especially when such genomes are large as is often the case in plants. Here, to shed light on the challenges of mapping sRNAs to TEs, we focus on the 2,300Mb maize genome, of which >85% is derived from TEs. We compare various methodological strategies that are commonly employed in TE studies. These include choices for the reference dataset, the normalization of multiple mapping sRNAs, and the selection among different types of sRNA metrics. We further examine how these choices influence the relationship between sRNAs and the critical feature of TE age, and explore and contrast their effect on low copy regions (exons) and other popular HTS data (RNA-seq). Finally, based on our analysis, we share a series of take-home messages to help guide TE epigenetic studies specifically, but our conclusions may also apply to any work that involves mapping and analysis of HTS data.
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Video Abstract (AI generated)
Paper
Preprint
In plants, self-fertilization is both an important reproductive strategy and a valuable genetic tool. In theory, selfing increases homozygosity at a rate of 0.50 per generation. Increased homozygosity can uncover recessive deleterious variants and lead to inbreeding depression, unless it is countered by the loss of these variants by genetic purging. Here we investigated the dynamics of purging on genomic scale by testing three predictions. The first was that heterozygous, putatively deleterious SNPs were preferentially lost from the genome during continued selfing. The second was that the loss of deleterious SNPs varied as a function of recombination rate, because recombination increases the efficacy of selection by uncoupling linked variants. Finally, we predicted that genome size (GS) decreases during selfing, due to the purging of deleterious transposable element (TE) insertions. We tested these three predictions by following GS and SNP variants in a series of selfed maize (Zea mays ssp. mays) lines over six generations. In these lines, putatively deleterious alleles were purged, and purging was more pronounced in highly recombining regions. Homozygosity increased more slowly than expected; instead of increasing by 50% each generation, it increased by 35% to 40%. Finally, three lines showed dramatic decreases in GS, losing an average of 398 Mb from their genomes over the short timeframe of our experiment. TEs were the principal component of loss, and GS loss was more likely for lineages that began with more TE and more chromosomal knob repeats. Overall, this study documented remarkable GS loss, as much DNA as three Arabidopsis thaliana genomes on average, in only a few generations of selfing.