Map-Based Cloning of the Quantitative Trait Locus Associated with Seed Dormancy and Flowering Time in Rice (Oryza sativa L.).

Seed dormancy, a key adaptive trait of both ecological and agricultural importance, co-evolved with some other adaptive or agronomic traits in rice (Oryza sativa L.) and its wild/weedy relatives. This research aimed to clone and characterize the qSD10 quantitative trait locus (QTL) for seed dormancy. A mapping population of about 4000 plants, which were derived from a cross between the indica line EM93-1 and its isogenic line for a qSD10-containing segment (<3 Mb) from the weedy rice line SS18-2, was genotyped to select recombinants to narrow the QTL. Progeny testing for selected recombinants allowed delimiting qSD10 to a genomic region of <150 Kb, which accounted for about 12% and 84% of the variances for seed dormancy and flowering time, respectively, with the allele from SS18-2 inhibiting germination and delaying flowering. The narrow genomic region contains the flowering-time gene Ehd1 (Os10g32600) encoding a Myb family transcription factor. RNAi analysis demonstrated that the transcription factor had pleiotropic effects on seed dormancy, plant height, and leaf and panicle morphologies, in addition to flowering time. These results demonstrated that the quantitative variation of seed dormancy in nature could be controlled by single genes with pleiotropic effects on flowering time and plant morphologies and also suggest that the qSD10 allelic variants could be used to manipulate modern cultivars for germination capability and its associated agronomic characteristics in crop breeding. Research is being conducted to identify allelic differentiation and distribution of the seed dormancy/flowering locus SD10/Ehd1 in the lineage of wild, weedy and cultivated rice and to determine cellular and molecular mechanisms that directly regulate the development or release of seed dormancy by SD10.