Séminaire Dr Arturo Marí-Ordóñez
Small meets smaller: rewiring small RNA silencing in duckweeds - Wednesday 4 November 2026 11 am, INRAE, Versailles
Small RNA pathways play important regulatory and genome defense roles in plants, 21-to-24-nt short interfering (si)RNAs and micro (mi)RNAs guide the silencing of transposable elements (TEs), viruses and endogenous genes, acting both at the transcriptional gene silencing level (TGS), through RNA-directed DNA methylation (RdDM), and post-transcriptionally gene silencing level (PTGS). Duckweeds unique reduced morphology and reproduction, and a wide gradient of genome size and TE content from the TE-poor Spirodela polyrhiza (~138 Mb, ~20% TEs) to the TE-rich Wolffia (~850 Mb, ~75% TEs), makes them a powerful comparative system to ask how a simplified body plan, a clonal lifestyle and contrasting genome organization shape plant RNA and epigenetic silencing.
Several studies have shown that duckweeds run a streamlined silencing machinery with uneven losses. The RdDM and transcriptional-silencing arm is simplified while the antiviral/PTGS arm lacks as well several key silencing factors. In Spirodela and Wolffia, this reduced toolkit still recognizes potentially mobile TEs: silencing and DNA methylation concentrate on young, intact elements, and the contrasting TE loads of the two species reorganize their small RNA and methylation landscapes accordingly. Across duckweeds, siRNAs of all size classes are frequently produced from the same loci, indicating that the pathways might be wired differently from the canonical pathways stablished in Arabidopsis rather than simply reduced.
The clearest difference lies in PTGS. In Arabidopsis, 22-nt siRNAs trigger transitivity, the small RNA mediated amplification of secondary siRNAs that spreads and boosts silencing in response to transgene overexpression and viruses among others. In duckweeds this appears strongly restricted: transgenes stay active with no PTGS and no transgene-derived siRNAs, and 22-nt siRNAs do not trigger canonical transitivity. Yet the machinery is not absent, duckweeds produce secondary siRNAs from miRNA targets, showing the pathway is functional. This suggests an apparent restriction of siRNA-mediated amplification rather than its loss. We will present our advances on understanding silencing and small RNA pathways in duckweeds and their deviation from canonical pathways described in other angiosperms, which makes them both a system to define the essential core of plant silencing and an attractive chassis for silencing-free transgene expression.
Arturo Marí-Ordóñez, Mechanisms of Recognition and Silencing of Transposons in Plants, "Gregor Mendel Institue for Molecular Plant Biology" GMI, "Austrian Academy of Sciences" ÖAW, Austria
Invitation: Martin Lacroix et Hervé Vaucheret, "Epigenetics and small RNAs" epiARN team
Seminar in connection with the research developed at the Institute Jean-Pierre Bourgin for Plant Sciences.
Several studies have shown that duckweeds run a streamlined silencing machinery with uneven losses. The RdDM and transcriptional-silencing arm is simplified while the antiviral/PTGS arm lacks as well several key silencing factors. In Spirodela and Wolffia, this reduced toolkit still recognizes potentially mobile TEs: silencing and DNA methylation concentrate on young, intact elements, and the contrasting TE loads of the two species reorganize their small RNA and methylation landscapes accordingly. Across duckweeds, siRNAs of all size classes are frequently produced from the same loci, indicating that the pathways might be wired differently from the canonical pathways stablished in Arabidopsis rather than simply reduced.
The clearest difference lies in PTGS. In Arabidopsis, 22-nt siRNAs trigger transitivity, the small RNA mediated amplification of secondary siRNAs that spreads and boosts silencing in response to transgene overexpression and viruses among others. In duckweeds this appears strongly restricted: transgenes stay active with no PTGS and no transgene-derived siRNAs, and 22-nt siRNAs do not trigger canonical transitivity. Yet the machinery is not absent, duckweeds produce secondary siRNAs from miRNA targets, showing the pathway is functional. This suggests an apparent restriction of siRNA-mediated amplification rather than its loss. We will present our advances on understanding silencing and small RNA pathways in duckweeds and their deviation from canonical pathways described in other angiosperms, which makes them both a system to define the essential core of plant silencing and an attractive chassis for silencing-free transgene expression.
Arturo Marí-Ordóñez, Mechanisms of Recognition and Silencing of Transposons in Plants, "Gregor Mendel Institue for Molecular Plant Biology" GMI, "Austrian Academy of Sciences" ÖAW, Austria
Invitation: Martin Lacroix et Hervé Vaucheret, "Epigenetics and small RNAs" epiARN team
Seminar in connection with the research developed at the Institute Jean-Pierre Bourgin for Plant Sciences.
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