Fig. 2

MiRNA modes of action in animals, plants and C. reinhardtii. Mature miRNAs are indicated in red, and mRNAs are in blue. The open reading frames of genes are represented with purple boxes. a In animals, mature miRNAs bind to the 3′UTR of their target mRNAs to trigger translation repression. The complementarity of animal miRNAs to their target mRNAs is imperfect: only the seed sequence (positions 2–8 of the miRNA) needs to be perfectly paired. Animal miRNAs often induce translational repression of targets by blocking translation initiation or elongation. b In plants, mature miRNAs bind to the coding region of their target mRNAs. Plant miRNAs typically exhibit near-perfect complementarity to their target mRNAs, leading to endonucleolytic slicing between positions 10 and 11 of miRNA/mRNA hybrids and subsequent degradation of the target mRNA. c In Chlamydomonas, mature miRNAs prefer to bind to the 3′UTR of their target mRNAs to trigger translation repression, similar to animal miRNAs. The complementarity of Chlamydomonas miRNAs to their target mRNAs is imperfect; perfect base pairing of the seed sequence is sufficient to induce moderate repression of target mRNAs