Plant roots show an impressive degree of plasticity in adaptingtheir branching patterns to ever-changing growth conditions.An important mechanism underlying this adaptation ability isthe interaction between hormonal and developmental signals.Here, we analyze the interaction of jasmonate with auxin toregulate lateral root (LR) formation through characterizationof an Arabidopsis thaliana mutant, jasmonate-induced defectivelateral root1 (jdl1/asa1-1). We demonstrate that, whereas exogenousjasmonate promotes LR formation in wild-type plants, it repressesLR formation in jdl1/asa1-1. JDL1 encodes the auxin biosyntheticgene ANTHRANILATE SYNTHASE 1 (ASA1), which is required for jasmonate-inducedauxin biosynthesis. Jasmonate elevates local auxin accumulationin the basal meristem of wild-type roots but reduces local auxinaccumulation in the basal meristem of mutant roots, suggestingthat, in addition to activating ASA1-dependent auxin biosynthesis,jasmonate also affects auxin transport. Indeed, jasmonate modifiesthe expression of auxin transport genes in an ASA1-dependentmanner. We further provide evidence showing that the actionmechanism of jasmonate to regulate LR formation through ASA1differs from that of ethylene. Our results highlight the importanceof ASA1 injasmonate-induced auxin biosynthesis and reveal arole for jasmonate in the attenuation of auxin transport inthe root and the fine-tuning of local auxin distribution inthe root basal meristem that is critical for lateral root formation.