A Raf‐Like MAPKKK Gene <i>TaHT1</i> Controls Drought Tolerance and Primary Root Length in Wheat

Wheat (Triticum aestivum L.) is one of the world's staple food crops, but it often suffers from water shortages during the growing season. Mitogen-activated protein kinase kinase kinases (MAPKKKs) are the critical signaling modules in plant drought response signaling pathways. However, the molecular mechanism of its involvement in wheat drought tolerance has not been fully elucidated. In the present study, we identified a novel wheat Raf-like MAPKKK high leaf temperature 1 (TaHT1) that interacts with sucrose non-fermenting 1-related protein kinase 2.10 (TaSnRK2.10), which plays a signaling hub role in drought stress response. TaHT1 is downregulated by polyethylene glycol (PEG) and abscisic acid (ABA) treatments. Ectopic expression of TaHT1 in rice (Oryza sativa) conferred short-root and drought-sensitive phenotype, the latter was manifested by increased malondialdehyde (MDA) accumulation, decreased cell membrane stability and plant survival rates under drought stress. TaHT1 regulates the expression of multiple genes involved in drought response and reactive oxygen species (ROS) scavenging pathways. In addition, sequence polymorphism and association analysis revealed that TaHT1-5B was significantly correlated with seedling primary root length. The superior haplotype Hap-5B-3 of TaHT1-5B with long primary root has been positively selected in the main wheat production zones in China wheat breeding history. Our study demonstrates that TaHT1 negatively regulates drought tolerance via its interaction with TaSnRK2.10, and its superior allele Hap-5B-3 and functional marker will provide valuable tools for wheat breeding.