Abstract
Heading date (flowering time) determines the adaptability of cultivars to different environments. We report the fine mapping and candidate gene analysis of qHD1b, a quantitative trait locus (QTL) responsible for early flowering that was derived from common wild rice (O. rufipogon) under both short-day and long-day conditions. The introgression line IL7391, which carried segments from common wild rice in a Zhonghui 8015 (ZH8015) background, exhibited early heading compared to the background and was crossed with ZH8015 to generate BC5F2:3 families for QTL analysis. This enabled the identification of two heading-date QTL, named qHD1b and qHD7, of which the first was selected for further research. High-resolution linkage analysis was performed in BC5F4:5 and BC5F6 populations, and the location of qHD1b was confined to a 112.7-kb interval containing 17 predicted genes. Five of these genes contained polymorphisms in the promoter or coding regions and were thus considered as candidates. Expression analysis revealed a positive association between LOC_Os01g11940 expression and early heading. This locus was annotated as OsFTL1, which encodes an ortholog of Arabidopsis Flowering Locus T and was the most likely candidate gene for qHD1b. Our study revealed that qHD1b acts as a floral activator that promotes flowering by up-regulating Ehd1, Hd3a, RFT1, OsMADS14, and OsMADS15 under both short-day and long-day conditions. Field experiments showed that qHD1b affected several yield-related agronomic traits including 1000-grain weight and grain length. qHD1b could be useful for marker-assisted selection and breeding of early-maturing cultivars.
