Drought-responsive TaMIP1 controls root density to confer the tradeoff between grain yield and drought resistance in wheat

Root density, determined by root number, is a key trait for drought resistance and yield improvement. Here, we identified a drought-responsive root number regulator, TabHLH112-2A, in wheat (Triticum aestivum). Given its interaction with the essential factor of crown root initiation, TaMOR, TabHLH112-2A was subsequently designated TaMIP1. mip1 mutants had fewer crown and lateral roots than the wild type (WT). TaMIP1 specifically bound to the E-box cis-element and induced the expression of genes involved in auxin and ABA signaling pathways, root development, and drought stress response. Two TaMIP1 haplotypes were found in the natural population. Two nonsynonymous SNPs in the active domain led to enhanced transactivation activity of TaMIP1Hap-2A-2, resulting in higher root dry weight. The TaMIP1 and TaMOR haplotypes had additive effects on RDW, and the effect of TaMOR haplotypes was epistatic to that of TaMIP1 haplotypes. Furthermore, mip1 exhibited a lower survival rate under drought stress and a higher yield under well-watered conditions. Our findings elucidate the important roles of TaMIP1 in root density and the tradeoff between yield and drought resistance. The discovery of a regulatory module and combined haplotypes bring insights and genetic resources for drought resistance and high-yield breeding.