期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 110, 期 46, 页码 18578-18583出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1310356110
关键词
ABC model; comparative gene expression; evo-devo; gigantism; parasitic plants
资金
- National Science Foundation Assembling the Tree of Life Grant [DEB-0622764]
- National Science Foundation [DEB-1120243]
- Division Of Environmental Biology
- Direct For Biological Sciences [1120243] Funding Source: National Science Foundation
Rafflesiaceae, which produce the world's largest flowers, have captivated the attention of biologists for nearly two centuries. Despite their fame, however, the developmental nature of the floral organs in these giants has remained a mystery. Most members of the family have a large floral chamber defined by a diaphragm. The diaphragm encloses the reproductive organs where pollination by carrion flies occurs. In lieu of a functional genetic system to investigate floral development in these highly specialized holoparasites, we used comparative studies of structure, development, and gene-expression patterns to investigate the homology of their floral organs. Our results surprisingly demonstrate that the otherwise similar floral chambers in two Rafflesiaceae subclades, Rafflesia and Sapria, are constructed very differently. In Rafflesia, the diaphragm is derived from the petal whorl. In contrast, in Sapria it is derived from elaboration of a unique ring structure located between the perianth and the stamen whorl, which, although developed to varying degrees among the genera, appears to be a synapomorphy of the Rafflesiaceae. Thus, the characteristic features that define the floral chamber in these closely related genera are not homologous. These differences refute the prevailing hypothesis that similarities between Sapria and Rafflesia are ancestral in the family. Instead, our data indicate that Rafflesia-like and Sapria-like floral chambers represent two distinct derivations of this morphology. The developmental repatterning we identified in Rafflesia, in particular, may have provided architectural reinforcement, which permitted the explosive growth in floral diameter that has arisen secondarily within this subclade.
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