A mini foxtail millet with an Arabidopsis -like life cycle as a C 4 model system

Foxtail millet ( Setaria italica ) is an important crop species and an emerging model plant for C 4 grasses. However, functional genomics research on foxtail millet is challenging because of its long generation time, relatively large stature and recalcitrance to genetic transformation. Here we report the development of xiaomi , a rapid-cycling mini foxtail millet mutant as a C 4 model system. Five to six generations of xiaomi can be grown in a year in growth chambers due to its short life cycle and small plant size, similar to Arabidopsis . A point mutation in the Phytochrome C ( PHYC ) gene was found to be causal for these characteristics. PHYC encodes a light receptor essential for photoperiodic flowering. A reference-grade xiaomi genome comprising 429.94 Mb of sequence was assembled and a gene-expression atlas from 11 different tissues was developed. These resources, together with an established highly efficient transformation system and a multi-omics database, make xiaomi an ideal model system for functional studies of C 4 plants.