Characterization and Fine Mapping of SiDWARF2 (D2) in Foxtail Millet

Elongation of grass internodes determines the plant height and underlies the grain yield of grass crop species, by enhancing of lodging resistance in elite cultivars. Foxtail millet [Setaria italica (L.) P. Beauv.] is an ancient cereal crop that served as a staple food during early civilization in China and is still grown widely across South and East Asia, Europe, and Africa. In this study, a foxtail millet dwarf mutant (Sidwarf2), derived from 'Yugu1', was characterized. In the dwarf mutant, significantly reduced cell lengths caused the observed shorter internodes. Gibberellin sensitivity analyses suggested that the height of the mutant could be restored under out spraying of gibberellic acid (GA(3)). In both the wild-type and the mutant, endogenous levels of GA(3) in elongated internodes stayed the same, while the abscisic acid (ABA) content of the dwarf mutant was greatly elevated. The dwarf gene (D2) was finally mapped on chromosome 3 and located to a genome region spanning 52.7 kb using combined bulked segregation analysis and map-based approaches. Twelve transcripts were annotated in the target region and a cytochrome P450 encoding gene was deduced to be the candidate gene of D2. This study highlighted the potential of fast-mapping-favorable loci in foxtail millet, which will aid molecular selection and modification of foxtail millet in the future.