Recombinant inbred lines and next-generation sequencing enable rapid identification of candidate genes involved in morphological and agronomic traits in foxtail millet

We constructed recombinant inbred lines (RILs) between a Japanese and a Taiwanese landrace of foxtail millet and employed next-generation sequencing, such as flexible ddRAD-seq and Nanopore sequencing to identify the candidate genes involved in the crop evolution of foxtail millet. We successfully constructed a linkage map using flexible ddRAD-seq with parents and RILs and detected major QTLs for each of three traits: leaf sheath colors, spikelet-tipped bristles (stb), and days to heading (DTH). (1) For leaf sheath colors, we identified the C gene on chromosome IV. (2) We identified a homeobox (HOX14) gene for stb on chromosome II, which shows homology with HvVrs1 in barley. (3) Finally, we identified a QTL with a large effect on DTH on chromosome II. A parent of the RILs from Taiwan and Yugu1 had a Harbinger-like TE in intron 3 of this gene. We also investigated the geographical distribution of the TE insertion type of this gene and found that the insertion type is distributed in the northern part of East Asia and intensively in South and Southeast Asia, suggesting that loss/reduction of function of this gene plays an important role in spreading into the northern part of East Asia and subtropical and tropical zones.