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Transposable elements and small RNAs contribute to gene expression divergence between Arabidopsis thaliana and Arabidopsis lyrata [RNA-Seq]

ABSTRACT: Transposable elements (TEs) are often the primary determinant of genome size differences among eukaryotes. In plants, the proliferation of TEs is countered through epigenetic silencing mechanisms that prevent transposition. Recent studies using the model plant Arabidopsis thaliana have revealed that methylated TE insertions are often associated with reduced expression of nearby genes, and these insertions may be subject to purifying selection due to their effect on nearby genes. Less is known about the genome-wide patterns of epigenetic silencing of TEs in other plant species. Here, we compare the 24-nt siRNA complement from Arabidopsis thaliana and a closely related congener with a two- to three-fold higher TE copy number, A. lyrata. We show that TEs, and particularly siRNA-targeted TEs, are associated with reduced gene expression within both species and also with gene expression differences between orthologs. In addition, A. lyrata TEs are targeted by a lower fraction of uniquely matching siRNAs, which are associated with more effective silencing of TE expression. Overall, our results suggest that the efficacy of RNA-directed DNA methylation silencing is lower in A. lyrata, a finding that may shed light on the causes of differential TE proliferation among species.

ORGANISM(S): Arabidopsis lyrata

PROVIDER: GSE24571 | GEO | 2011/02/11

SECONDARY ACCESSION(S): PRJNA132411

REPOSITORIES: GEO

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Transposable elements and small RNAs contribute to gene expression divergence between Arabidopsis thaliana and Arabidopsis lyrata [RNA-Seq]

Project description:Transposable elements (TEs) are often the primary determinant of genome size differences among eukaryotes. In plants, the proliferation of TEs is countered through epigenetic silencing mechanisms that prevent transposition. Recent studies using the model plant Arabidopsis thaliana have revealed that methylated TE insertions are often associated with reduced expression of nearby genes, and these insertions may be subject to purifying selection due to their effect on nearby genes. Less is known about the genome-wide patterns of epigenetic silencing of TEs in other plant species. Here, we compare the 24-nt siRNA complement from Arabidopsis thaliana and a closely related congener with a two- to three-fold higher TE copy number, A. lyrata. We show that TEs, and particularly siRNA-targeted TEs, are associated with reduced gene expression within both species and also with gene expression differences between orthologs. In addition, A. lyrata TEs are targeted by a lower fraction of uniquely matching siRNAs, which are associated with more effective silencing of TE expression. Overall, our results suggest that the efficacy of RNA-directed DNA methylation silencing is lower in A. lyrata, a finding that may shed light on the causes of differential TE proliferation among species. 4 A. lyrata mRNA-seq samples

2011-02-11 | E-GEOD-24571 | biostudies-arrayexpress

Euchromatic transposon insertions trigger production of novel pi- and endo-siRNAs at the target sites in the Drosophila germline

Project description:The control of transposable element (TE) activity in germ cells provides genome integrity over generations. A distinct small RNA-mediated pathway utilizing Piwi-interacting RNAs (piRNAs) suppresses TE expression in gonads of metazoans. In the fly, primary piRNAs derive from so-called piRNA clusters, which are enriched in damaged repeated sequences. These piRNAs launch a cycle of TE and piRNA cluster transcript cleavages resulting in the amplification of piRNA and TE silencing. Using genome-wide comparison of TE insertions and ovarian small RNA libraries from two Drosophila strains, we found that individual TEs inserted into euchromatic loci form novel dual-stranded piRNA clusters. Formation of the piRNA-generating loci by active individual TEs provides a more potent silencing response to the TE expansion. Like all piRNA clusters, individual TEs are also capable of triggering the production of endogenous small interfering (endo-si) RNAs. Small RNA production by individual TEs spreads into the flanking genomic regions including coding cellular genes. We show that formation of TE-associated small RNA clusters can down-regulate expression of nearby genes in ovaries. Integration of TEs into the 3' untranslated region of actively transcribed genes induces piRNA production towards the 3'-end of transcripts, causing the appearance of genic piRNA clusters, a phenomenon that has been reported in different organisms. These data suggest a significant role of TE-associated small RNAs in the evolution of regulatory networks in the germline. The fractions of small RNAs (19-29 nt) from ovaries of y[1]; cn[1] bw[1] sp[1] line of Drosophila melanogaster were sequenced using Illumina HiSeq 2000.

2014-02-07 | E-GEOD-46105 | biostudies-arrayexpress

Euchromatic transposon insertions trigger production of novel pi- and endo-siRNAs at the target sites in the Drosophila germline

2014-02-07 | GSE46105 | GEO

Dynamic co-evolution of transposable elements and the piRNA pathway in East African cichlid fishes

Project description:East African cichlid fishes have radiated in an explosive fashion. The (epi)genetic basis for the abundant phenotypic diversity of these fishes remains largely unknown. As transposable elements (TEs) contribute extensively to genome evolution, we reasoned that TEs may have fuelled cichlid radiations. While TE-derived genetic and epigenetic variability has been associated with phenotypic traits, TE expression and epigenetic silencing remain unexplored in cichlids. Here, we profiled TE expression in African cichlids, and describe dynamic expression patterns during embryogenesis and according to sex. Most TE silencing factors are conserved and expressed in cichlids. We describe an expansion of two truncated Piwil1 genes in Lake Malawi/Nyasa cichlids, encoding a Piwi domain with catalytic potential. To further dissect epigenetic silencing of TEs, we focused on small RNA-driven epigenetic silencing. We detect a small RNA population in gonads consistent with an active Piwi-interacting RNA (piRNA) pathway targeting TEs. We uncover fluid genomic origins of piRNAs in closely related cichlid species. This, along with signatures of positive selection in piRNA pathway factors, points towards fast co-evolution of TEs and the piRNA pathway. Our study is the first step to understand the contribution of ongoing TE-host arms races to the cichlid radiations in Africa.

2024-04-02 | PXD047439 | Pride

Complex Genetic Interactions between Piwi and HP1a in the Repression of Transposable Elements and Tissue-Specific Genes in the Ovarian Germline

Project description:Insertions of transposable elements (TEs) in eukaryotic genomes are usually associated with repressive chromatin, which spreads to neighbouring genomic sequences. In ovaries of Drosophila melanogaster, the Piwi-piRNA pathway plays a key role in the transcriptional silencing of TEs considered to be exerted mostly through the establishment of H3K9me3 histone marks recruiting Heterochromatin Protein 1a (HP1a). Here, using RNA-seq, we investigated the expression of TEs and the adjacent genomic regions upon Piwi and HP1a germline knockdowns sharing a similar genetic background. We found that the depletion of Piwi and HP1a led to the derepression of only partially overlapping TE sets. Several TEs were silenced predominantly by HP1a, whereas the upregulation of some other TEs was more pronounced upon Piwi knockdown and, surprisingly, was diminished upon a Piwi/HP1a double-knockdown. We revealed that HP1a loss influenced the expression of thousands of protein-coding genes mostly not adjacent to TE insertions and, in particular, downregulated a putative transcriptional factor required for TE activation. Nevertheless, our results indicate that Piwi and HP1a cooperatively exert repressive effects on the transcription of euchromatic loci flanking the insertions of some Piwi-regulated TEs. We suggest that this mechanism controls the silencing of a small set of TE-adjacent tissue-specific genes, preventing their inappropriate expression in ovaries.

2021-12-22 | GSE186867 | GEO

Pervasive epigenetic effects of Drosophila euchromatic transposable elements impact their evolution [RNA-seq]

Project description:We study the relatively unexplored evolutionary consequences of the epigenetic effects of transpoable elements (TEs) by providing the first genome-wide quantification of such effects in wild-derived D. melanogaster and D. simulans strains. Surprisingly, over half of euchromatic TEs show spread of repressive epigenetic marks to nearby DNA, resulting in differential epigenetic states of homologous genic alleles and, in return, selection against TEs. Interestingly, compared to D. melanogaster, the lower TE content in D. simulans is correlated with stronger epigenetic effects of TEs and higher levels of host genetic factors known to promote epigenetic silencing. We conclude that the epigenetic effects of euchromatic TEs, and host genetic factors modulating such effects, play a critical role in the population dynamics of TEs within and between species.

2017-07-01 | GSE94741 | GEO

Pervasive epigenetic effects of Drosophila euchromatic transposable elements impact their evolution [ChIP-seq]

2017-07-01 | GSE94735 | GEO

Transcriptional activity and epigenetic regulation of transposable element in the symbiotic fungus Rhizophagus irregularis

Project description:Arbuscular mycorrhizal (AM) fungi form mutualistic relationships with most land plant species. AM fungi have long been considered as ancient asexuals. Long-term clonal evolution would be remarkable for a eukaryotic lineage and suggests the importance of alternative mechanisms to promote genetic variability facilitating adaptation. Here, we assessed the potential of transposable elements (TEs) for generating genomic diversity. The dynamic expression of TEs during Rhizophagus irregularis spore development suggests ongoing TE activity. We find Mutator-like elements located near genes belonging to highly expanded gene families. Characterising the epigenomic status of R. irregularis provides evidence of DNA methylation and small RNA production occurring at TE loci. Our results support a potential role for TEs in shaping the genome, and roles for DNA methylation and small RNA-mediated silencing in regulating TEs. A well-controlled balance between TE activity and repression may therefore contribute to genome evolution in AM fungi.

2022-02-17 | PXD025245 | Pride

Epigenetic reprogramming and small RNA silencing of transposable elements in pollen.

Project description:The mutagenic activity of transposable elements (TEs) is suppressed by epigenetic silencing and small interfering RNAs (siRNAs), especially in gametes that would transmit transposed elements to the next generation. In pollen from the model plant Arabidopsis, we show that TEs are unexpectedly reactivated and transpose, but only in the pollen vegetative nucleus, which accompanies the sperm cells but does not provide DNA to the fertilized zygote. TE expression coincides with down-regulation of the heterochromatin remodeler DECREASE IN DNA METHYLATION 1 and of most TE siRNAs. However, 21 nucleotide siRNA from Athila retrotransposons is generated in pollen and accumulates in sperm, indicating that siRNA from TEs activated in the vegetative nucleus can target silencing in gametes. We propose a conserved role for reprogramming in germline companion cells, such as nurse cells in insects and vegetative nuclei in plants, to reveal intact TEs in the genome and regulate their activity in gametes.

2014-09-04 | GSE61028 | GEO

Control of agricultural traits by hc-siRNA associated MITEs in rice

Project description:Transposable elements (TEs) and repetitive sequences comprise over 40% of rice genome. Different TEs are tightly regulated by distinct epigenetic mechanisms. For example, the activities of LTR retrotransposon Tos17 and non-LTR retrotransposon LINE element Karma are uniquely regulated by histone H3K9 methylation and histone H3K4 demethylation, respectively. Miniature inverted repeat transposable elements (MITEs) are one of the most high-copy-number DNA transposons, which are interspersed around rice genome and might influence nearby gene expression. In plants, 24-nucleotide (24-nt) heterochromatic small interfering RNAs (hc-siRNAs) derived from repeats and TEs. To what extent hc-siRNA associated TEs affect gene expression and therefore contribute to agricultural traits in rice remains elusive. Here, we show that OsDCL3a, one of Dicer-Like 3 (DCL3) homolog, is primarily responsible for 24-nt hc-siRNA processing in rice. Impaired OsDCL3a displayed altered important agricultural traits in rice. We found that genome-wide (281,563) 24-nt hc-siRNA clusters were OsDCL3a-dependent, among which MITEs were significantly enriched. Impaired OsDCL3a caused significant overlapping between reduced hc-siRNAs from MITEs and elevated nearby gene expression. Intriguingly, genes involved in Gibberellin and Brassinosteroid homeostasis were identified as direct targets of OsDCL3a, which may attribute to dwarfism and enlarged flag leaf angle upon OsDCL3a deficiency. Our work uncovers OsDCL3a-dependent hc-siRNAs derived from MITEs as broad spectrum of regulators for fine-tuning gene expression, and this observation may reflect a conserved mechanism in other higher plants with dispersed repeat- or TE-rich genomes. Examination of OsDCL3a-dependent hc-siRNAs derived from MITEs.

2014-02-04 | E-GEOD-50778 | biostudies-arrayexpress

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