Emergence and diversification of sRNA pathway proteins in plants. A) The major clades of Viridiplantae examined in this study. B) Number of species sampled from each clade. C) Presence (filled circle) or absence (white circle) of sRNA pathway proteins. D) Refined evolutionary history of DCL/RDR/AGO proteins. Dashed white lines indicate the absence of DCL/RDR/AGO proteins in specific lineages.