Population Transcriptome and Phenotype Reveal that theRht-D1bContribute a Larger Seedling Roots to Modern Wheat Cultivars

ABSTRACT The crop root system is pivotal for water and nutrient uptake. Although the breeding selection significantly increased the yield of modern wheat cultivars, then how this selection reshapes the root system remains largely unknown. Here we performed a large-scale transcriptomic and phenotypical investigations on the seedling root of 406 wheat accessions, which demonstrated modern cultivars (MC) had significantly changed in the root transcriptome and root development. The MC had a significantly larger seedling root system than that in landraces (LA), and this was mainly due to the Rht-D1b allele introduction. Physiological and cytological investigations showed that the Rht-D1b suppressed gibberellin (GA) signaling, thus inhibiting the cell length in above-ground tissue but increasing the cell length in roots. This distinct regulation of GA signaling between above- and under-ground tissues contributed to MC having a significantly larger root-shoot ratio. Moreover, Rht-D1b also has a GA-independent role to enlarge root cell width that enhanced the root diameter, ultimately contribute to a larger root surface and volume to MC seedlings. These findings provide new insights to understand the successful application of GA-suppressing alleles in modern wheat breeding and its futural application to form a robust wheat root system. Short Summary Rht-D1b is the major allele that contribute a larger root system and higher root-shoot ratio to modern wheat cultivars.