Hold a leaf up to the light and its complex vascular system or venation stands out clearly. Little is known about how leaf vascular development is spatially regulated, except that auxin signalling is involved. Now, on p. 1699, Koizumi and colleagues report that vesicle transport mediated by VAN3, an ADP-ribosylation factor-GTPase activating protein (ARF-GAP), is involved in leaf vein pattern formation in Arabidopsis. The Arabidopsis mutant van3 has a discontinuous vein pattern, and, using double-mutant analyses, the researchers show that VAN3 is involved in auxin signal transduction. They identify VAN3 as a gene encoding a unique type of ARF-GAP and localise VAN3 to a subpopulation of the trans-Golgi network (TGN). The researchers conclude that VAN3 functions in vein pattern formation by regulating auxin signalling via a TGN-mediated transport system, thus uncovering the first developmental role for an ARF-GAP in plants.