Kawai, T.; Kitomi, Y.; Kuroda, R.; Nakata, R.; Iba, M.; Soma, F.; Teramoto, S.; Yamazaki, T.; Sugimoto, K.; Uga, Y.

Drought considerably affects crop productivity, and its severity is being intensified by climate change. Therefore, enhancing drought resistance is a crucial priority in crop breeding for ensuring sustainable agriculture. The root system architecture (RSA) influences the efficiency of water acquisition from land; therefore, a deep RSA is advantageous for avoiding drought stress. Here, we demonstrated that deeper RSA promoted by the qSOR1-v mutant allele (an enhanced functional allele of the quantitative trait locus for SOIL SURFACE ROOTING 1) significantly improves rice yield under drought when compared to the deep RSA achieved through the functional qSOR1 allele that originated from natural variation. The qSOR1-v mutant exhibited stronger root gravitropism than the wild type. This was characterized by a more pronounced polarization of auxin on the lower side during root curvature, leading to a robust vertical rooting phenotype that was consistently expressed across different soil-water environments. Additionally, the qSOR1-v mutation site was well conserved among angiosperm orthologs, and the corresponding mutation in LZY3 of Arabidopsis (qSOR1 ortholog) resulted in a steeper root growth angle. The rice introgression line, which was substituted from the functional qSOR1 allele to qSOR1-v through marker-assisted selection, showed vertical rooting, resulting in increased grain yield in an upland field under drought stress. No yield penalty was observed for this line under well-watered upland conditions than the original variety. These findings highlight the potential of qSOR1-v and corresponding mutations in angiosperm orthologs to promote vertical rooting across plant species, which can help sustain crop yields in drought-prone areas.