Characterization of a FLORICAULA/LEAFY homologue of Gnetum parvifolium andits implications for the evolution of reproductive organs in seed plants

The morphological variation among reproductive organs of extant seed plants makes assessment of organ homology difficult. Comparisons of expression pa tterns of homeotic genes that control organ development will yield new info rmation about the homology of organs to assess inferences deduced from prev ious morphological studies. In angiosperms, the FLORICAULA/LEAFY (FLO/LFY) genes convert a vegetative shoot meristem to a floral meristem by inducing floral homeotic genes, most of which belong to the MADS-box gene family. To provide insights into the evolution of reproductive organs in seed plants, a FLO/LFY homologue (GpLFY) was cloned from Gnetum parvifolium. GpLFY mRNA was expressed in both the vegetative shoot apex and the female strobilus. The GpLFY mRNA signal was detected in early developmental stages of the col lar and the ovule primordium, including the nucellus and three envelopes. A comparison of FLO/LFY gene expression in Gnetum and the conifer Pinus radi ata indicates that the Gnetum collar and ovule are homologous with the coni fer bract and ovule-ovuliferous scale complex, respectively. Overexpression of GpLFY in transgenic Arabidopsis promoted a conversion of a shoot merist em to a floral primordium. The Arabidopsis LFY null mutant, lfy-26, with a malformed flower, was complemented by overexpression of GpLFY. These result s indicate that the inductive pathway from the FLO/LFY gene to the MADS-box genes already existed in the common ancestor of angiosperms and gymnosperm s.