Rapid and reversible root growth inhibition by TIR1 auxin signalling

The phytohormone auxin is the information carrier in a plethora of developmental and physiological processes in plants(1). It has been firmly established that canonical, nuclear auxin signaling acts through regulation of gene transcription(2). Here we combined microfluidics, live imaging, genetic engineering and computational modeling to reanalyze the classical case of root growth inhibition(3) by auxin. We show that Arabidopsis roots react to addition and removal of auxin by extremely rapid adaptation of growth rate. This process requires intracellular auxin perception but not transcriptional reprogramming. The formation of the canonical TIR1/AFB-Aux/IAA co-receptor complex is required for the growth regulation hinting to a novel, non-transcriptional branch of this signaling pathway. Our results challenge the current understanding of root growth regulation by auxin and suggest another, presumably non-transcriptional signaling output of the canonical auxin pathway.