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Pelton Award Lecture

Friedman, William E. [1].

A generation forgotten and Goethe remembered: Modularity and the evolution of flowering plants.

Two hundred and fifteen years after Goethe first elucidated the modular nature of the sporophyte and the serial homology of leaves and floral organs ("Alles ist Blatt"), plant structural innovation through metamorphosis of basic modules can now be extended to the gametophyte generation. The angiosperm female gametophyte is constructed of basic four-nucleate modular subunits. Moreover, evolutionary transitions in the number and developmental patterning of these modular subunits directly alter the genetic constitution of endosperm (ploidy and maternal to paternal genomic ratios). This insight, coupled with evolutionary developmental analysis, indicates that the first angiosperm female gametophytes were composed of a single (four-celled) module, which upon double fertilization yielded a diploid endosperm. Very early in angiosperm history (within 15 million years of the common ancestor of crown group flowering plants), ectopic expression of this basic developmental module resulted in the production of two developmental modules within the female gametophyte. The result was the formation of the "typical" seven-celled/eight-nucleate structure that yields a triploid endosperm with the 2:1 maternal to paternal genome ratio characteristic of most flowering plants. This modular concept can be extended to show that all major changes in endosperm ploidy (from derived diploid, as in Oenothera, to pentaploid in disparate clades, to pentadecaploid in Piperaceae) are ultimately tied to changes in the number and developmental patterning of the basic angiosperm female gametophyte module. Finally, a parable about the dangers of believing what is reported in the literature, particularly in the review literature, will be told.


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1 - University of Colorado, Department of Ecology and Evolutionary Biology, UCB 334, Boulder, Colorado, 80309, USA

Keywords:
Goethe
modularity
gametophyte
endosperm
angiosperms
development
evolution.

Presentation Type: Special Presentation
Session: 11-1
Location: Salon B - Gov Ballroom/Hilton
Date: Monday, August 15th, 2005
Time: 11:00 AM
Abstract ID:308


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