Inhibition of RNA polymerase II allows controlled mobilisation of retrotransposons for plant breeding.
Sunday, 2017/08/06 | 06:13:28
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Thieme M, Lanciano S, Balzergue S, Daccord N, Mirouze M, Bucher E. Genome Biol. 2017 Jul 7;18(1):134. doi: 10.1186/s13059-017-1265-4. AbstractBACKGROUND:Retrotransposons play a central role in plant evolution and could be a powerful endogenous source of genetic and epigenetic variability for crop breeding. To ensure genome integrity several silencing mechanisms have evolved to repress retrotransposon mobility. Even though retrotransposons fully depend on transcriptional activity of the host RNA polymerase II (Pol II) for their mobility, it was so far unclear whether Pol II is directly involved in repressing their activity. RESULTS:Here we show that plants defective in Pol II activity lose DNA methylation at repeat sequences and produce more extrachromosomal retrotransposon DNA upon stress in Arabidopsis and rice. We demonstrate that combined inhibition of both DNA methylation and Pol II activity leads to a strong stress-dependent mobilization of the heat responsive ONSEN retrotransposon in Arabidopsis seedlings. The progenies of these treated plants contain up to 75 new ONSEN insertions in their genome which are stably inherited over three generations of selfing. Repeated application of heat stress in progeny plants containing increased numbers of ONSEN copies does not result in increased activation of this transposon compared to control lines. Progenies with additional ONSEN copies show a broad panel of environment-dependent phenotypic diversity. CONCLUSIONS:We demonstrate that Pol II acts at the root of transposon silencing. This is important because it suggests that Pol II can regulate the speed of plant evolution by fine-tuning the amplitude of transposon mobility. Our findings show that it is now possible to study induced transposon bursts in plants and unlock their use to induce epigenetic and genetic diversity for crop breeding.
See https://www.ncbi.nlm.nih.gov/pubmed/28687080
Figure 2: Simultaneous inhibition of DNA methyltransferases and Pol II reduces global CHH methylation and mimics the TE silencing deficiency of the nrpd1 background. a Genome-wide DNA methylation levels in the WT after CS and CS plus treatment with A (5 μg/ml), Z (40 μM), or a combination of A and Z (A&Z) for three sequence contexts (brown for CG, yellow for CHG and blue for CHH). b Same as a but only depicting the CHH context for clarity. c Methylome data of treated and untreated plants at an ONSEN locus located on Chr 1 (ONSEN is indicated in yellow, its LTRs in red). d Northern blot of ONSEN transcripts directly after CS, HS and HS plus treatment with A, Z or a combination of A&Z in the WT and after HS in nrpd1 plants. The black arrow indicates the ONSEN full-length transcript. Below, a Midori-stained agarose gel is shown as a loading control. e ONSEN copy number measured by qPCR directly after CS and HS treatments in WT, rdr6, dcl2/3/4 and nrpd1 seedlings directly after CS, HS and HS plus treatment with A, Z or a combination of A&Z (mean ± s.e.m, n = 3 biological repetitions, values relative to ACTIN2; *P < 0.05, **P < 0.01). |
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