A plant microRNA regulates the adaptation of roots to drought stress

► The Arabidopsis mutant fry1 is sensitive to ABA in the inhibition of lateral root growth and has a higher level of miR393. ► ABA decreases the expression of the wild-type but not miR393-resistant AFB2. ► ABA or osmotic stress no longer inhibits lateral root growth of miR393-resistant plants. Plants tend to restrict their horizontal root proliferation in response to drought stress, an adaptive response mediated by the phytohormone abscisic acid (ABA) in antagonism with auxin through unknown mechanisms. Here, we found that stress-regulated miR393-guided cleavage of the transcripts encoding two auxin receptors, TIR1 and AFB2, was required for inhibition of lateral root growth by ABA or osmotic stress. Unlike in the control plants, the lateral root growth of seedlings expressing miR393-resistant TIR1 or AFB2 was no longer inhibited by ABA or osmotic stress. Our results indicate that miR393-mediated attenuation of auxin signaling modulates root adaptation to drought stress.