|Budget Amount *help
¥14,600,000 (Direct Cost : ¥14,600,000)
Fiscal Year 1998 : ¥3,300,000 (Direct Cost : ¥3,300,000)
Fiscal Year 1997 : ¥11,300,000 (Direct Cost : ¥11,300,000)
A flower is the most complex reproductive organ in land plants and composed of sepals, petals, stamens, and gynoecium (s).Haploid cells, mega and microspores, for syngamy are formed by meiosis in a stamen and a gynoecium.Microspores are enclosed in a multicellular sporangium.Megaspores develop in a nucellus covered with inner and outer integuments.Gymnosperms and ferns have simpler reproductive organs than anigiosperms and lack sepals and sepals.A nucellus of a gymnosperm is covered with only one integument, while sporangiums of ferns have no integuments and are naked on the abaxial side of a leaf.
The development of floral organs is mainly regulated by the members of the MADS gene family whose members are transcription factors containing conserved MADS and K domains.MADS genes of angiosperms are divided into more than 10 groups based on the
gene tree, while MADS genes of the fern Ceratopteris richardii are classified into 3 groups whose relationships to angiosperm MADS genes are ambiguo
us with low bootstrap values.Based on the studies of three gymnosperms, Pinus, Ginkgo and Gnetum, almost all groups of angiosperm MADS genes have been differenciated, suggesting that increase of MADS gene number is likely to be related to the evolution of complexed reproductive organs in plants.
In angiosperms, some MADS genes are expressed in specific floral organ primordia as homeotic selector genes, while other MADS genes are expressed in both reproductive and vegetative organs.In gymnosperms, reproductive-organ-specific expression of MADS genes have been reported.Like the latter type of angiosperm MADS genes, most of the fern MADS genes are expressed in both the reproductive and vegetative organs.The generally-expressed MADS genes may be more primitive than the reproductive organ-specific MADS genes.If so, it is likely that some of the MADS genes were co-opted as homeotic selector genes of specialized reproductive organs and their expression restricted to specific floral organ primordia, events that occurred after the divergence of ferns and seed plants.The restriction of MADS gene expression may have been caused by the evolution of other genes that regulate the MADS genes.
These recent results may indicate that (1) the increase of MADS genes via gene duplication, (2) the restriction of expression of some MADS genes to specific reproductive organs, and (3) the specialization of MADS gene functions as homeotic selector genes in the angiosperm lineage were important in the floral organ evolution of vascular plants. Less