Figure 1: (a) Schematic representation of a typical miRNA hairpin showing the position of the lower DCL processing site (filled and open dark gray arrowheads), upper DCL processing site (filled and open gray arrowheads), and the positions of potential mature miRNA or miRNA* (filled and open arrowheads, resp.). (b) Primary and predicted secondary structures of stem-loop elements in Bryophyta and Marchantiophyta miR390 precursors. Sequences of the highly conserved AGCU tetranucleotides at the lower DCL processing sites of miRNA or miRNA* are underlined. Names of plant species with sequenced portions limited by conserved AGCU tetranucleotides are underlined.