The effects of the plant hormone auxin have been widely stud-ied over many decades.Auxin regulates diverse processes in plants,and auxin signaling is known to play key roles in both plant development and plant response to environmental cues(Paque and Weijers,2016).To date,most of the reports dealing with perturbations of auxin signaling relied on auxin sensors based on transcriptional readouts (i.e.,changes in the output level of the reporter.due to transcriptional effects of auxins).These sensors,mostly based on the DR5 or the DII reporter systems,have enabled broad characterization of auxin distributions under various developmental or stress conditions.However,known drawbacks of these reporters include their slow activation,irreversibility,and,most importantly,not directly sensing auxin.Recently,Herud-Sikimi(c) et al.(2021) reported a F(o)rster resonance energy trans-fer (FRET)-based auxin biosensor that relies on direct auxin binding.