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Fig. 5. Hypothetical signals specifying leaf polarity in the meristem.
miR166 (blue) accumulates most strongly below the incipient leaf (I1, white
dashed line) and in a graded pattern in I1 and older primordia (P1, P2). Such
a gradient might be formed by the movement of miR166 itself or may be directed
by a secondary mobile signal. A hypothetical lipid signal (red), possibly
required for HD-ZIPIII activity, is predicted to act in the meristem (M). If
such a lipid contributes to the Sussex signal, it might be restricted to the
L1 layer, as shown. The distribution of auxin within the primordia and stem
(green), as inferred from the localization of AUX1 and PIN1
(Reinhardt et al., 2003),
could contribute to abaxial fate through either ETT and/or
ARF4 or perhaps MIR166. Notice that the distributions of
auxin within the leaf are speculative. tasi-ARFs (yellow) might also regulate
leaf polarity non-cell autonomously, possibly by moving out of the meristem
tip, where SGS3/lbl1 is expressed.
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