Fig. 4. Genetic interactions that establish adaxial-abaxial polarity in leaves. Pathways are divided into those contributing to adaxial versus abaxial fate and those involving protein components (A) versus the biogenesis and activity of small RNAs (sRNAs) (B). Direct interactions are distinguished from indirect and putative (dashed line) interactions by bold arrows and lines. On the left are false-colored meristems representing generalized expression patterns across plant lineages. The colors of the expression domains correspond to the colors of the factors that they represent.