A heading date QTL, qHD7.2, from wild rice (Oryza rufipogon) delays flowering and shortens panicle length under long-day conditions

Heading date (HD) and panicle length (PL) are important traits that affect rice breeding and are controlled by pleiotropic genes. Some alleles associated with HD and PL from wild relatives might differ from those in cultivated rice. In this study, a main effect HD quantitative trait locus from wild rice, qHD7.2, was identified using a chromosomal segment substitution line (CSSL) population. First, qHD7.2 was determined to be located near RM172 on chromosome 7 based on association analysis of phenotype data from six environments and 181 polymorphic molecular markers. CSSL39, which has the latest flowering of all CSSLs and carries qHD7.2, was selected for further study, and qHD7.2 was narrowed to a 101.1-kb interval using a CSSL39/9311 F(2) population. An OsPRR37-homologous gene was found within this region. The wild type allele delayed flowering and shortened PL under long-day conditions. The HD7.2, which was identified as a candidate gene for qHD7.2, transcript level was substantially higher than that in 9311. Our data showed that HD7.2 is likely a novel OsPRR37 allele. Sequence analysis revealed that OsPRR37 in cultivated rice had multiple origins, and natural variation in the coding domain sequence and promoter region contribute to flowering time diversity in cultivated rice.