Foxtail millet (Setaria italica) is a drought-tolerant C4 cereal that grows on marginal lands and serves as a nutrient-rich food for millions in Asia and Africa. Despite its resilience and nutritional value, the genetic basis underlying plant height variation in foxtail millet remains incompletely understood, thereby constraining the effective implementation of semi-dwarfing strategies analogous to those that drove the Green Revolution in major cereals. This study identified sidt1, a semi-dwarf, high-tillering mutant exhibiting a compact architecture and enhanced lodging resistance. It is demonstrated that SiDT1 encodes a GA3-oxidase orthologous to rice D18/XIAOWEI. A single A-to-T mutation disrupted its catalytic function, reducing bioactive gibberellin biosynthesis. CRISPR-Cas9 knockout lines recapitulated the sidt1 phenotype, confirming SiDT1's functional role. Combined transcriptomic profiling and SiD53 immunoblot analysis indicated that strigolactone-related signaling is perturbed in sidt1, in agreement with its enhanced tillering phenotype. Notably, under high-density planting conditions, sidt1 maintained grain yield and quality while exhibiting superior lodging resistance. These findings identify SiDT1 as a key regulator of plant architecture and establish a semi-dwarf ideotype reminiscent of the rice Green Revolution, providing a valuable genetic resource for high-density and mechanized foxtail millet production.
