The rice mutant mp3 was derived from an indica–japonica cross between Rejing35 and XieqingzaoB, producing an inconstant number of pistils ranging from one to four pistils in a floret at heading stage, which also developed an open-glume with one or two seeds and twin seedlings at mature and seedling stage. Several altered characteristics, including filling grain panicle–1 (62.90), grain-setting rate (60.48%) and grain yield plant–1 (13.42 g), decreased but an increase in 1000-grain weight (36.87 g) was observed. Genetic analysis revealed that the mp3 mutant phenotype was controlled by a single recessive gene. Using a chromosome walking strategy in the F2 population of 02428/mp3, the mp3 gene was fine mapped between L3-135 and RM7576, with a physical distance of 30.617 kb on rice chromosome 3. Four candidate genes were found in this region referred to the rice genome annotations. LOC_Os03g11614/OsMADS1 corresponded with the mutant mp3 phenotype. Sequencing showed no sequence alterations in the coding and promoter sequence of the LOC_Os03g11614/OsMADS1 of mp3. The mp3 gene may be an allelic gene with three previously reported genes but controlled different mutant floral organ phenotypes in rice. Therefore, this mp3 gene provided a novel perspective on the biological function of OsMADS1 in the development of rice floral organ.
