Transposable elements (TEs) are DNA sequences with the ability to mobilize, potentially causing harmful effects on the integrity of the host genome. In plants, the regulation of these elements occurs through the RNA-directed DNA methylation (RdDM) pathway, a mechanism extensively studied in Arabidopsis thaliana. Expanding the scope of molecular studies to non-model organisms offers opportunities to uncover alternative regulatory pathways.
Duckweed, being the smallest and fastest-growing flowering plant serves as an attractive biological model for both basic research and biotechnological applications. Notably, essential components of the RdDM pathway are either absent or expressed at low levels in the duckweed genome. Consequently, the genome methylation patterns and small RNA abundance and size distribution in duckweeds differ significantly from those observed in Arabidopsis. These distinctions make duckweeds an ideal candidate for investigating alternative TE regulatory mechanisms.
In plants, transgenes can undergo recognition and silencing through mechanisms similar to those of TEs. To investigate the gene silencing mechanisms in duckweeds, we established transformation protocols in Spirodela polyrrhiza (transiently) and Lemna minor (stably). Upon Spirodela and Lemna transformation, the subsequent analysis of the small RNAs produced and loaded into Argonaute proteins revealed the presence of 21- and 22-nt small RNAs, but not 24-nt ones, targeting boths constructs. Given the absence of DCL2, these findings raise questions about the biogenesis of these 22-nt small RNAs. To further investigate these silencing mechanisms we will be the use Crispr technology in the stable transgenic lines in Lemna.