In plants, the dorsoventral (DV) boundary of leaves defines an axis of symmetry separating the dorsal (top) and ventral (bottom) tissues. Intriguingly cells located at this boundary appear to act as an organizer to control leaf orientation and morphology analogously to DV and anteriorposterior (AP) boundaries in the Drosophila wing imaginal disk. A gap of one to two cells in width separating the dorsally expressed REVOLUTA and ventrally expressed KANADI transcription factors is thought to define this boundary as a zone of localised auxin activity, potentially due to the absence of repression by these transcription factors. However our recent mosaic experiments reveal that REV clones induce auxin signalling and leaf blade outgrowth at clonal boundaries, even without a gap between REV and KAN expression being present. This juxtaposition-dependent signalling and development parallels findings in the fly wing, demonstrating that a similar overall logic is at work. We are currently testing several candidate signals that may be downstream of REV function and our latest results will be reported.