Developmental and Structural Section
Bachelier, Julien , Friedman, William .
Female gametophyte competition in early-diverging lineages of flowering plants.
Just over the last twenty years, molecular studies have greatly contributed to the resolution of the phylogenetic relationships amongst flowering plants at all systematic levels. In addition, the resolution of a basal grade of three early-diverging lineages, referred to as the ANITA grade, provided a new and robust framework for ancestral character reconstruction, which revealed that the first flowering plants were surprisingly far more diverse than it was long assumed. Recently, we reported in Trimenia,an extant member of the ANITA grade, a remarkable mechanism of female gametophyte development. In each ovule, multiple female gametophytes are differentiated remotely from the site of fertilization and they initiate a pattern of intercellular tip growth in the nucellus central tissue. They grow concurrently like tubes, intertwined with each other from the base to the apex of the nucellus, and only one of them will yield the unique embryo of each seed. Sucha development strikingly resembles that of pollen tubes growing in the transmitting tissue of the carpel, and suggests that Trimenia has evolved a unique mechanism of female gametophyte competition. However,our phylogenetic analysis reveals that such a mechanism is not unique in angiosperms and that it may be variously expressed. For instance, the initiation of multiple female gametophytes exhibiting a pattern of tip growth is rare in angiosperms and only occurs in a few unrelated taxa, whereas the occasional production of more than one female gametophyte is frequent is some extant members of the ANITA-grade and other basal clades. Therefore, a mechanism of female gametophyte (egg) competition may have played a central role in the reproductive biology of the first flowering plants and, in addition to male gametophyte (sperm) competition and maternal mate choice, may have contributed to their rapid diversification and tremendous diversity.
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1 - Harvard University, Arnold Arboretum - Organismic And Evolutionary Biology, 1300TH CENTRE STREET, BOSTON, MA, 02131, USA
2 - University Of Colorado, DEPT OF EPO BIOLOGY, Boulder, CO, 80309-0334, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Portland Room/Chase Park Plaza
Date: Wednesday, July 13th, 2011
Time: 8:45 AM