tComplex flowers containing large numbers of petals are especially prized as ornamental plants. Double-flowered Tricyrtis macranthopsis, in which stamens and carpels are converted to petaloid organs, is relatedto AGAMOUS (AG) gene expression. So we isolated AGAMOUS gene from T. macranthopsis, named asTrimAG. Since TrimAG expression was limited to whorls 3 and 4 and ectopic expression of TrimAG inArabidopsis thaliana caused the same phenotype as overexpression of other AG orthologs in transgenicArabidopsis, this gene has similar function as its AG orthologs. In the double-flowered T. macranthop-sis cultivar, the level of TrimAG expression was reduced in the two inner reproductive whorls (stamensand carpels) and caused reproductive organ replacement with petaloid tepals and floral indeterminacy.Southern blot analysis of genomic DNA indicated that there were no significant differences between thedouble-flowered cultivar and wild-type plants. Analysis of promoter and AG intron II sequences did notidentify any critically mutated sequences in the doubled-flowered cultivar. These results suggest thatreduced TrimAG expression in whorls 3 and 4 might be caused by mutation in one of the genes in regula-tory network which controls AGAMOUS expression or transcriptional silencing by methylation of TrimAGpromoter/intron sequences

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