Found: The missing discriminators of cell-surface auxin receptors.

An Arabidopsis cell-surface auxin receptor that mediates rapid elongation consists of transmembrane kinases (TMKs) and an auxin-binding co-receptor. Auxin-binding protein 1 (ABP1) is one identified TMK co-receptor, but abp1 mutants have no elongation phenotypes. Yu et al. use structural analysis of the ABP1-binding pocket to identify functional ABP1-like (ABL) TMK co-receptors that regulate rapid growth.