MicroRNAs (miRNAs) are small RNAs, 21 to 22 nucleotides long, with important regulatory roles. They are
processed from longer RNA molecules with imperfectly matched foldback regions and they function in
modulating the stability and translation of mRNA. Recently, we and others have demonstrated that the
unicellular alga Chlamydomonas reinhardtii, like diverse multicellular organisms, contains miRNAs. These
RNAs resemble the miRNAs of land plants in that they direct site-specific cleavage of target mRNA with
miRNA-complementary motifs and, presumably, act as regulatory molecules in growth and development.
Utilizing these findings we have developed a novel artificial miRNA system based on ligation of DNA
oligonucleotides that can be used for specific high-throughput gene silencing in green algae.