How a Retrotransposon Exploits the Plant's Heat Stress Response for Its Activation

Abstract

Retrotransposons are major components of plant and animal genomes. They amplify by reverse transcription and reintegration into the host genome but their activity is usually epigenetically silenced. In plants, genomic copies of retrotransposons are typically associated with repressive chromatin modifications installed and maintained by RNA-directed DNA methylation. To escape this tight control, retrotransposons employ various strategies to avoid epigenetic silencing. Here we describe the mechanism developed by ONSEN, an LTR-copia type retrotransposon in Arabidopsis thaliana. ONSEN has acquired a heat-responsive element recognized by plant-derived heat stress defense factors, resulting in transcription and production of full length extrachromosomal DNA under elevated temperatures. Further, the ONSEN promoter is free of CG and CHG sites, and the reduction of DNA methylation at the CHH sites is not sufficient to activate the element. Since dividing cells have a more pronounced heat response, the extrachromosomal ONSEN DNA, capable of reintegrating into the genome, accumulates preferentially in the meristematic tissue of the shoot. The recruitment of a major plant heat shock transcription factor in periods of heat stress exploits the plant's heat stress response to achieve the transposon's activation, making it impossible for the host to respond appropriately to stress without losing control over the invader.

Transposable elements contribute to activation of maize genes in response to abiotic stress

“…Tissue culture has been shown to result in activation of transposons and retrotransposons in a number of plant species [30]- [31]. There are also examples of transcriptional activation of TEs in response to specific abiotic stresses in tobacco [22], rice [26]- [27] and Arabidopsis [16], [28]- [29]. It is expected that the stress The relative expression levels in stress compared to control treatments (log 2 ratio) is shown for B73, Mo17, and Oh43 for each of the 10 expressed genes that are polymorphic for insertions of TEs.…”

“…The rice DNA transposon mPing can be activated in response to cold and salt stress [26]- [27]. The Arabidopsis retrotransposon ONSEN is transcriptionally activated by heat stress [16], [28]- [29]. Tissue culture is a complex stress that can result in the activation of DNA transposons in maize and retrotransposons in rice [30]- [31].…”

Creating Order from Chaos: Epigenome Dynamics in Plants with Complex Genomes

“…For example, the ONSEN retrotransposon promoter lacks CG and CHG sites, which may limit the ability of the host to stably silence this element via DNA methylation (Cavrak et al, 2014). Similarly, many MITE transposons are exceptionally AT-rich and sometimes prefer to insert into AT-rich regions (Le et al, 2000;Naito et al, 2009).…”

Polyploidy and novelty: Gottlieb's legacy

“…Because TEs can change their position within a genome, they are considered important factors associated with genome reorganization and epigenetic changes [73,74]. Furthermore, transposon activity can be influenced by either environmental stress [75,76] or genomic changes, including polyploidy [77]. In polyploids, changes in transposon activity are twofold, with effects on both transcriptional activity and transpositional activity.…”