Studies on the origin of angiosperms and the evolution of ovules

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1.A morphological analysis of ovules of Magnolia grandiflora, Magnoliaceae, was performed in order to understand the morphology of the primitive ovule of angiosperms. The outer integument arose as a hood-shaped structure and then became cupular with an outgrowth arising on the funiculus between a gap in the integument. In the ovules of three families assigned to the primitive order Austrobaileyales, the outer integument is hood-shaed in Austrobaileya and Ttimernia, while it is copular in Illicium. Taking in account data of other primitive angiosperms and phylogenetic relationships of angiosperms, it is inferred that the primitive ovule is the anatropous one with the hood-shaped outer integument, which is similar to the lateral organ leaf.2.In order to better understand the homology of the ovule and that of the integument of primitive angiosperms at gene level, expression patterns were analyzed for homologues of genes of the YABBY family, which are involved in determination of the dorsiventrality of lateral organs. NaINO, an INO homologue, isolated from Nymphaea, Nymphaeaceae, was expressed in the outer layer of the outer integument. The result suggested that the outer integument may be a lateral organ homologous to the leaf. AmbF1, a YABBY2 homologue, isolated from Amborella, was expressed in the dorsal tissue of the leaf and the inner tissue of the carpet, patterns distinct from those of the advanced eudicot Arabidopsis thaliana, a model plant. These results are not in accordance with the widely accepted hypotheses that the carpel is a con duplicate leaf or an ascidiate structure derived from a peltate leaf.3.In conclusion, it is inferred the outer integument unique to angiosperms arose from a lateral organ such as the leaf and then diversified, and NaINO and AmbF1 homologous to YABBY family genes that govern the specificity of lateral organs evolved and their expression patterns changed in association with the origin and diversification of angiosperms.