Early-diverging angiosperms show most of the diversity in arrangement and number of floral parts in angiosperms. Elucidating the genetics of floral development in these lineages will provide key insights into the early evolution of the flower. We isolated, sequenced, and characterized the expression of B class genes from Eupomatia bennettii (Eupomatiaceae; Magnoliales). Eupomatia bennettii has flowers that bear a calyptra, an unusual organ whose structural homology and derivation are unknown, although some have proposed it is a bract. Sequences of APETALA3 were determined from E. bennettii (EbAP3). Two EbAP3 sequences were present, differing by one nucleotide at the third codon position. Phylogenetic analysis of protein sequences of EbAP3s and previously reported MADS box genes grouped the AP3 gene of E. bennettii with MfAP3 (Michelia figo) and LtAP3 (Liriodendron tulipifera), both also of Magnoliales. This relationship in AP3 genes is identical to that inferred from molecular phylogenetic analyses of early-diverging angiosperms using multiple genes. An inter-exon primer pair, specific for EbAP3 mRNA, was designed from the EbAP3 gene sequences. Using this primer pair, the expression level of EbAP3 was measured in each floral organ (calyptra, stamen, staminode, and carpel) using relative quantitative RT-PCR to address the question of the origin of the calyptra.

Key words: APETALA3, B class genes, calyptra, EbAP3, Eupomatia bennettii, MADS box, relative quantitative RT-PCR