LAUSR

Plant roots exhibit plasticity in their branching patterns to forage efficiently for heterogeneously distributed resources, such as soil water. The xerobranching response represses lateral root formation when roots lose contact with water. Here, we show that xerobranching is regulated by radial movement of the phloem-derived hormone abscisic acid, which disrupts intercellular communication between inner and outer cell layers through plasmodesmata. Closure of these intercellular pores disrupts the inward movement of the hormone signal auxin, blocking lateral root branching. Once root tips regain contact with moisture, the abscisic acid response rapidly attenuates. Our study reveals how roots adapt their branching pattern to heterogeneous soil water conditions by linking changes in hydraulic flux with dynamic hormone redistribution. Description Lateral root development Plant roots are most effective in pockets of soil containing the water that the plant needs. Water is not uniformly distributed throughout the soil, and the xerobranching response, in which lateral root formation is suppressed, ensures that roots are not uniformly distributed either. Mehra et al. show what happens as plant roots grow into and through dry pockets in soil. In moist conditions, water flows from the root surface into the phloem, but in a dry spot, water flows instead from the phloem out into the root tissues. This reverse flow carries along the phloem-derived hormone abscisic acid, which closes off intercellular pores, blocking the ability of the hormone auxin to initiate lateral root development. —PJH Transient water stress suppresses root branching by linking changes in hydraulic flux with dynamic hormone redistribution.