Acyl acid amido synthetases of the GH3 family act as critical pre-receptor modulators of plant hormone action; however, the molecular basis for their hormone selectivity is unclear. Recent crystal structures of GH3 proteins (Westfall et al., 2012 Science 336, 1708) combined with biochemical analysis define how a highly adaptable three-dimensional scaffold is used for the evolution of promiscuous activity across an enzyme family for modulation of plant signaling molecules.