A root-cap-specific transcriptional network controls root hair elongation and nutrient foraging.

Root hairs (RHs) are critical for nutrient acquisition, yet the mechanisms by which their elongation is calibrated to environmental cues remain poorly understood. While the lateral root cap (LRC) physically encases the root tip, its potential regulatory role in determining the fate of the neighboring epidermis has been largely overlooked. In this study, we demonstrate that the persistence of LRC is required for a transient signaling hub that remotely controls RH elongation in Arabidopsis. The LRC-localized NAC transcription factor SOMBRERO acts as the integrative hub of an auxin-driven communication pathway between the LRC and epidermis. Specifically, ANAC033/SOMBRERO (SMB) coordinates auxin transport and biosynthesis by regulating the expression of AUX1 and the indole-3-butyric acid (IBA)-to-IAA conversion gene ECH2, which cooperatively create auxin maxima in the epidermis to drive RH elongation. Furthermore, we showed that SOMBRERO is required for maintaining basal expression levels of genes associated with RH development and acquisition of nitrogen and phosphorus, thereby regulating the RH responses to external nutrient conditions. Our findings uncover a non-cell-autonomous mechanism within the LRC through which SMB activates a precise transcriptional circuit that is coordinated with the LRC developmental program to optimize RH foraging strategies under fluctuating environments.