Fig. 6.

Plant-specific insertions within the Dicer Platform subdomain increased RNA affinity in DCL2, DCL3, and DCL1 lineages. We measured the binding kinetics of ancestral Platform + PAZ + Connector (PPC) domains to synthetic RNAs modeling microRNAs or viralRNAs (see Materials and Methods; RNA sequences are shown in supplementary fig. S10, Supplementary Material online). We plot steady-state binding (pKd, light bars) and initial binding rates (pKm, dark bars) to each RNA, with longer bars indicating tighter binding. Standard errors are shown, with kinetics curves shown in supplementary figs. S11 and S18, Supplementary Material online. We introduced the historical RN927Δ deletion (black dotted outline) in concert with DCL3-, DCL2-, and DCL1-specific α3–β4 (red dotted outline) and α4–α5 (blue dotted outline) loop regions into the ancAnimal/Plant/Fungi Dicer background (see figs. 2 and 3) and plot the structural orientation of each Dicer protein (green ribbon) bound to RNA (red ribbon), inferred by structural homology modeling (see Materials and Methods). Protein regions too diverged from the structural template to ensure reliable modeling are indicated by dotted lines.