Fig. 9. Genetic pathway leading to adaxial cell fate and mediolateral growth of the maize leaf. lbl1 and miRNA166 have an opposing affect on the accumulation of rld1 transcripts, and together lead to the adaxial specific expression of rld1. RLD1 specifies adaxial cell fate, possibly upon activation by the proposed meristem-derived signal. RLD1 also induces yabby gene expression in the adaxial domain, and the juxtaposition of yabby-expressing and non-expressing cells mediates mediolateral outgrowth.