Model for YAB function during the early stages of leaf development. Adaxial-abaxial patterning is established during the early stages of leaf development and is closely associated with the onset of FIL/YAB3 expression. FIL/YAB3 maintain KAN1 and ARF4 expression through direct positive regulation, which in turn establishes a positive feedback loop. As well as acting as positive regulators, YABs associate with transcriptional co-repressors, forming a repressive complex that potentially targets adaxial-promoting factors. It is likely that this regulatory network is confined to the early stages of leaf development, as at later stages FIL/YAB3 expression is present at high levels in the margins of the growing lamina, but KAN1 expression is not readily detectable.