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

Cultivating high-yield wheat under limited water resources is crucial 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 studies and transcriptome profiling, we identified a wheat atypical basic helix-loop-helix(b HLH) transcription factor(TF), Tab HLH27-A1, as a promising quantitative trait locus candidate for both relative root dry weight and spikelet number per spike in wheat. Tab HLH27-A1/B1/D1 knockout reduced wheat drought tolerance, yield, and water use efficiency(WUE). Tab HLH27-A1 exhibited rapid induction with polyethylene glycol(PEG) treatment, gradually declining over days. It activated stress response genes such as Ta CBL8-B1 and Ta CPI2-A1 while inhibiting root growth genes like Ta SH15-B1 and Ta WRKY70-B1 under short-term PEG stimulus. The distinct transcriptional regulation of Tab HLH27-A1 involved diverse interacting factors such as Ta ABI3-D1 and Tab ZIP62-D1. Natural variations of Tab HLH27-A1influence its transcriptional responses to drought stress, with Tab HLH27-A1Hap-IIassociated with stronger drought tolerance, larger root system,more spikelets, and higher WUE in wheat. Significantly, the excellent Tab HLH27-A1Hap-IIwas selected during the breeding process in China,and introgression of Tab HLH27-A1Hap-IIallele improved drought tolerance and grain yield, especially under water-limited conditions. Our study highlights Tab HLH27-A1's role in balancing root growth and drought tolerance, providing a genetic manipulation locus for enhancing WUE in wheat.