ON THE COVER

Both polar auxin transport and vesicle cycling are inhibited by synthetic auxin transport inhibitors, such as 1-N-naphthylphthalamic acid (NPA); however, underlying targets and mechanisms are unclear. By using NMR and in silico docking, Zhu et al. (pages 930–948) mapped the NPA binding surface on the chaperone of an ABCB-type auxin transporter, TWISTED DWARF1 (TWD1), and identified ACTIN7 as a relevant TWD1 interactor. TWD1 determines downstream locations of auxin efflux transporters by adjusting actin filament debundling and dynamizing processes and mediates NPA action on the latter. The cover shows increased cortical actin bundling of hypocotyls upon NPA treatments visualized using the GFP-fABD2 actin marker (green fluorescence). Quantum chemical analysis of the electron density components identifies the NPA contact region (electronic density deformation for NPA in orange and red and for the amino acid residues in cyan and blue).