Auxin plays a role to induce cell proliferation during graft-union processes, however the molecular mechanism has not yet been clarified. In this issue, Matsuoka et al. (on pp. 2620—2631) report that auxin promotes cell proliferation of vascular tissue via the upregulation of ANAC071/ANAC096 and expansion of cortex cells by promoting gibberellin biosynthesis during graft attachment in Arabidopsis hypocotyls.