Recent studies have shown that F-box proteins constitute a large family in eukaryotes andplay pivotal roles in regulating various developmental processes in plants.However, their functionsin monocots are still obscure.In this study,we characterized a recessive mutant dwarf anddeformed Jlowerl-1(ddfl-1)in rice.The mutant is abnormal in both vegetative and reproductivedevelopment,with significant size reduction in all organs except spikelet.DDFI controls organsize by regulating both cell division and cell expansion. In the ddfl-1spikelet,the specification offloral organs in whorls 2 and 3 is altered,with most lodicules and stamens being transformed intoglume-like organs and pistil-like organs,respectively;but the specification of lemmalpalea andpistil in whorls 1and4 is not affected.DDFI encodes an F-box protein anchored in nucleolus andis expressed in almost all vegetative and reproductive tissues.Consistent with the mutant floralphenotype,DDFI positively regulates B-class genes OsMADS4/16,and negatively regulates pistilspecification gene DL.In addition,DDFI also negatively regulates the Arabidopsis LFY orthologAP02,implicating a functional connection between DDFI and AP02.Collectively,these resultsrevealed thatDDFl,as a newly identified F-box gene,is a crucial genetic factor with pleiotropicfunctions for both vegetative growth and floral organ specification in rice.These findings provideadditional insights into the molecular mechanism controlling monocot vegetative and reproductivedevelopment.