Auxin/ ROS ‐Mediated Coordination of Lateral Root and Root Hair Development in Wheat ( Triticum aestivum L.) Under Low‐Temperature Stress

Low temperature is a common stressor for winter field crops, notably impacting wheat roots. However, there is scarce knowledge on subterranean wheat root responses to low temperatures. To address this knowledge gap, we investigated the adaptive responses and underlying mechanisms of wheat roots to cold stress using a hydroponic system. Our investigation revealed that 4°C stress alters wheat root system architecture (RSA) by inhibiting primary and lateral root growth while increasing root hair density and length. Transcriptomic analysis identified auxin (IAA) and reactive oxygen species (ROS) as potentially crucial regulatory factors in the adaptation of wheat roots to low temperatures. Furthermore, a protein interaction network links ROS metabolism and auxin signaling, with NADPH-dependent thioredoxin reductase A (NTRA) serving as a central regulatory node. Pharmacological manipulation (utilizing IAA and polar transport inhibitors) and histochemical localization experiments demonstrated that the interplay between lateral roots and root hairs under low-temperature stress is associated with the spatial distribution of IAA in the epidermis and stele. Time-course analysis indicated that ROS function as early signaling molecules that initiate downstream IAA signaling pathways. Pharmacological intervention using ROS scavengers and histochemical localization experiments revealed that scavenging ROS disrupts the epidermal distribution of auxin, consequently impeding root hair development. We propose a model termed "ROS-IAA spatio-temporal coordination mediates RSA plasticity." In this model, the low-temperature-induced ROS surge acts as an upstream trigger for auxin redistribution, ultimately balancing the trade-off between lateral root inhibition and root hair promotion. These findings enhance our comprehension of auxin responsiveness and RSA plasticity in wheat root adaptation to low temperatures, offering theoretical underpinning for leveraging wheat roots as a target for breeding climate-resilient varieties.