Comprehensive identification of major flowering time genes and their combinations, which determined rice distribution in Northeast China

Flowering time of rice (Oryza sativa L.) is among the most important agronomic traits for regional adaptation and grain yield. To date, a number of genes or quantitative trait loci (QTLs) controlling flowering time have been identified in rice, and diverse natural allelic variations for these flowering genes have been revealed, which suggested that the underlying regulation mechanism of flowering time in rice is very complicated. Northeast China is a major cultivation region for temperate japonica rice, where the temperature is cooler and the day length is longer. The regional adaptability of local rice cultivar is substantially different from that of other regions. Recently, some flowering genes have been proved to play roles in regulating flowering time of local cultivars. However, a comprehensive analysis of the effectiveness of these flowering genes has not been performed. In the present study, 395 cultivars collected from Northeast China is re-sequenced, SNP and InDel markers were called for 23 selected flowering-related genes. The heading date of these cultivars was also investigated for three consecutive years. Through association analysis, we found that Hd2, Hd4, and Hd5 are major flowering repressors, whereas Dth2 and Hd18 are major flowering promoters. Furthermore, Hd6 and Hd16 were identified as minor flowering repressors, and Hd17 was minor flowering promoter, in that their effectiveness can exclusively be detected when both Hd2 and Hd4 are functional. Collectively, we comprehensively identified the major and minor flowering genes which determine flowering time of temperate japonica rice grown in Northeast China.