Flower origin
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document in English
biology
presentation
published 11/11/2008
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Summary
Since the identity of floral organs is specified by conserved floral organ-identity genes, clarifying the phylogeny of these genes and their protein products may provide us with valuable insights into the evolution of flowers. Analysis of numerous MADS box genes from mosses and ferns suggested that orthologues of floral homeotic genes are absent in non-seed plants. However, orthologues of class B and class C floral homeotic genes were identified in different conifers and in the gnetophyte Gnetum gnemon, orthologues of class C floral homeotic genes were also reported for Cycas and Ginkgo. This suggests that B- and C-type genes were established by gene duplications and sequence divergence in the lineage that led to extant seed plants, after the lineage that led to extant ferns had already branched off, i.e. 300–400 million years ago, even though some molecular clock estimates suggested a considerably earlier origin of these genes.
Table of Contents
- Introduction.
- Flower origin.
- The expression patterns of gymnosperm B and C genes.
- Differential expression of B genes specifying male organ identity.
- Floral diversification.
- Organ identity.
- The perigon of Liliaceae.
- Petaloid organs in Ranunculaceae.
- Conclusion.
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