In plants, transposable elements (TEs) are predicted targets of endogenous microRNAs (miRNAs), suggesting that miRNA-TE interactions could represent an ancient evolutionary force driving epigenetic regulation and genome expansion. This includes the highly conserved miR845 family that targets specifically retrotransposons in Arabidopsis pollen, in a mechanism that has been implicated in the regulation of parental genome dosage in triploid seeds [1]. However, the role of miR845 in epigenome reprogramming and TE evolution remains poorly understood. Interestingly, natural variation in miR845 activity was observed in Arabidopsis thaliana, where the loss of miR845 correlates with increased TE expression in pollen and low triploid seed abortion [1]. In addition, within the Brassicaceae family, we have recently confirmed the absence of functional MIR845 genes in Arabis alpina, where a massive genome expansion resulted from increased activity of predicted miR845 targets [2]. In order to investigate the role of miR845 in these species, we have generated MIR845 complementation lines of A. thaliana Ler-0 and A. alpina, which were able to restore strong miR845 expression in pollen. I will present our preliminary small RNA and transcriptome analysis of these lines, where we expect to find important mechanistic insight on the role of miR845 in the epigenetic control of TEs during reproduction and seed development. Ultimately, we expect that this work will allow to elucidate the impact of miR845 in the evolution and expansion of retrotransposons in plant genomes.

References:

1 Borges, F.; Parent, J.-S.; Van Ex, F.; Wolff, P.; Martínez, G.; Köhler, C.; Martienssen, R.A. Transposon-Derived Small RNAs Triggered by MiR845 Mediate Genome Dosage Response in Arabidopsis. Nat. Genet. 2018, 50, 186–192. https://doi.org/10.1038/s41588-017-0032-5

2 Willing, E.-M. et al. Genome expansion of Arabis alpina linked with retrotransposition and reduced symmetric DNA methylation. Nat Plants. 2015, 1, 14023. https://doi.org/10.1038/nplants.2014.23