TabHLH27 orchestrates root growth and drought tolerance to enhance water use efficiency in wheat

Cultivating high-yield wheat under limited water resources is essential for sustainable agriculture in semiarid regions. Amid water scarcity, plants activate drought response signaling, yet the delicate balance between drought tolerance and development remains unclear. Through genome-wide-association study (GWAS) and transcriptome profiling, we identified a wheat atypical basic helix-loop-helix (bHLH) transcription factor (TF), TabHLH27-A1, as a promising quantitative trait locus (QTL) candidate for both relative root dry weight (DW.R%) and spikelet number per spike (SPS) in wheat. TabHLH27-A1/B1/D1 knockout reduced wheat drought tolerance, yield, and water use efficiency (WUE). TabHLH27-A1 exhibited rapid induction with PEG treatment, gradually declining over days. It activated stress response genes such as TaCBL8-B1 and TaCPI2-A1 while inhibiting root growth genes like TaSH15-B1 and TaWRKY70-B1 under short-term PEG stimulus. The distinct transcriptional regulation of TabHLH27-A1 involved diverse interacting factors such as TaABI3-D1 and TabZIP62-D1. Natural variations of TabHLH27-A1 influences its transcriptional responses to drought stress, with TabHLH27-A1Hap-II associated with stronger drought tolerance, larger root system, more spikelets, and higher WUE in wheat. Significantly, the elite TabHLH27-A1Hap-II was selected during the breeding process in China, and introgression of TabHLH27-A1Hap-II allele improves drought tolerance and grain yield, especially under water-limited conditions. Our study highlights TabHLH27-A1's role in balancing root growth and drought tolerance, providing a genetic manipulation locus for enhancing WUE in wheat.