Expression of Artificial MicroRNAs in Physcomitrella patens

MicroRNAs (miRNAs) are ∼21-nt-long small RNAs transcribed from endogenous MIR genes which form precursor RNAs with a characteristic hairpin structure. MiRNAs control the expression of cognate target genes by binding to reverse complementary sequences resulting in cleavage or translational inhibition of the target RNA. Artificial miRNAs (amiRNAs) can be generated by exchanging the miRNA/miRNundefined sequence of endogenous MIR precursor genes, while maintaining the general pattern of matches and mismatches in the foldback. Thus, for functional gene analysis, amiRNAs can be designed to target any gene of interest. During the last decade, the moss Physcomitrella patens emerged as a model plant for functional gene analysis based on its unique ability to integrate DNA into the nuclear genome by homologous recombination which allows for the generation targeted gene knockout mutants. In addition to this, we developed a protocol to express amiRNAs in P. patens that has particular advantages over the generation of knockout mutants and might be used to speed up reverse genetics approaches in this model species.