RNA silencing in plants has been studied the most in angiosperms, but Adrian A. Valli and colleagues at the University of Cambridge, UK, have recently investigated the process in the single-cell alga Chlamydomonas reinhardtii using a forward genetic screen.
They used a light-induced cell death reporter system to identify RNA silencing mutants, and characterized three of them with mutations of the DCL3 gene. Genetic complementation of the mutants confirmed that DCL3 has a central role in the biogenesis of both miRNAs and siRNAs. DCL3 differs from plant DCLs but has some limited similarity to the Drosha protein involved in animal miRNA biogenesis.
The DCL3-dependent siRNAs derive from coding genes or transposable elements, as in higher plants. The miRNAs, however, are unlike their higher plant counterparts in that they are generated mostly from introns or untranslated regions of coding RNAs rather than non-coding regions. Another difference is that the C. reinhardtii miRNAs and siRNAs are not negative regulators of mRNA accumulation. The only mRNAs to over-accumulate in the dcl3 mutants were those that had an miRNA precursor structure in the untranslated region.
The unique features of RNA silencing in C. reinhardtii provide insight into the evolution and function of this pathway in eukaryotes.
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Lyu, J. RNA silencing: Machinery in algae. Nature Plants 2, 16070 (2016). https://doi.org/10.1038/nplants.2016.70
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DOI: https://doi.org/10.1038/nplants.2016.70
