Biology subjects

Trasser, M.

Publications and source records attributed to Trasser, M..

3 recordsLinked to original sources

bioRxiv2024

PTGS is dispensable for the initiation of epigenetic silencing of an active transposon in Arabidopsis

Transposable elements (TEs) are largely repressed in plants through transcriptional gene silencing (TGS), which is maintained by heritable epigenetic silencing marks such as DNA methylation. However, the mechanisms by which silencing is installed in the first place remains poorly understood in plants. Small interfering (si)RNAs and post-transcriptional gene silencing (PTGS) play a role in the initial response by reducing mRNA and protein levels of active TEs and are believed to mediate the initiation of TGS by guiding the first deposition of DNA methylation. To determine how this silencing installation works, we took advantage of EVADE (EVD), an endogenous retroelement in Arabidopsis, which can be used to recapitulate true de novo silencing with a well-established sequence of PTGS followed by a TGS phase. To test whether PTGS is a prerequisite for TGS, active EVD copies were introduced into RNA-DEPENDENT-RNA-POLYMERASE-6 (RDR6) mutants lacking an essential PTGS component. EVD activity and silencing were monitored across several generations. Unexpectedly, even in the absence of PTGS, TGS and silencing of EVD were still achieved through installation of RNA-directed DNA methylation (RdDM) at EVD regulatory sequences without any prior DNA methylation at its coding sequence. Hence, our study shows that PTGS is dispensable for de novo EVD silencing. Although we cannot rule out that PTGS might facilitate the initiation of TGS, or control TE activity until then, initiation of epigenetic silencing can take place in its absence.

plant biology↗

bioRxiv2021

Innate, translation-dependent silencing of an invasive transposon in Arabidopsis

Co-evolution between hosts and parasites genomes shapes diverse pathways of acquired immunity based on silencing small (s)RNAs. In plants, sRNAs cause heterochromatinization, sequence-degeneration and, ultimately, loss-of-autonomy of most transposable elements (TEs). Recognition of newly-invasive plant TEs, by contrast, involves an innate antiviral-like silencing response. To investigate this responses activation, we studied the single-copy element EVADE (EVD), one of few representatives of the large Ty1/Copia family able to proliferate in Arabidopsis when epigenetically-reactivated. In Ty1/Copia-elements, a short subgenomic mRNA (shGAG) provides the necessary excess of structural GAG protein over the catalytic components encoded by the full-length genomic flGAG-POL. We show here that the predominant cytosolic distribution of shGAG strongly favors its translation over mostly-nuclear flGAG-POL, during which an unusually intense ribosomal stalling event coincides precisely with the starting-point of sRNA production exclusively on shGAG. mRNA breakage occurring at this starting-point yields unconventional 5OH RNA fragments that evade RNA-quality-control and concomitantly likely stimulate RNA-DEPENDENT-RNA-POLYMERASE-6 (RDR6) to initiate sRNA production. This hitherto-unrecognized "translation-dependent silencing" (TdS) is independent of codon-usage or GC-content and is not observed on TE remnants populating the Arabidopsis genome, consistent with their poor association, if any, with polysomes. We propose that TdS forms a primal defense against de novo invasive TEs that underlies their associated sRNA patterns.

plant biology↗

bioRxiv2019

Understory light quality affects leaf pigments and leaf phenology in different plant functional types

Understory plant species take on different functional strategies, whereby some exploit periods of available light in springtime before the canopy closes, and others also benefit from sunlight later in autumn when the canopy opens again. These strategies involve understory species coordinating phenological events to pre-empt canopy leaf out and to extend their growing season beyond canopy leaf senescence, meanwhile accumulating photo-protective pigments which mitigate periods of high-light exposure. Canopy closure brings shade to the understory, but also causes drastic changes in light quality. Whilst many experiments manipulating spectral quality have revealed understory plant responses to the changing R:FR ratio in shade, effect of the blue and UV regions have been examined very little. We installed filters attenuating short wavelength regions of the solar spectrum in a forest understory in southern Finland, creating the following treatments: a transparent control filter, and filters attenuating UV radiation < 350 nm, all UV radiation, and both UV and blue light. In eight understory species, representing different plant functional types, we repeatedly assessed leaf optical properties to obtain epidermal flavonol and anthocyanin contents from leaf emergence in spring to leaf senescence in autumn, during both 2017 and 2018. Flavonols responded more to seasonal changes in light quality in relatively light-demanding species than in shade-tolerant and wintergreen species; and were particularly responsive to blue light. However, anthocyanins were largely unaffected by our filter treatments, suggesting that other cues such as cold temperatures govern their seasonal variation. UV radiation only accelerated leaf senescence in Acer platanoides seedlings, but blue light accelerated leaf senescence in all species measured apart from Quercus robur. In summary, seasonal changes in understory solar radiation in the blue and UV regions affected leaf pigments and leaf phenology; particularly for more light-demanding species. An increase in canopy duration under climate change will extend the period of shade in the understory, with consequences for the spectral cues available to understory plants. The resultant reduction in blue and UV radiation in shade, could delay leaf senescence in the understory even further.

plant biology↗