The ABCs of floral homeotic genes
Homeotic mutants, that is, mutants with a normal organ in a place where an organ of another type is typically found, were first recognized in plants. The earliest descriptions of mutants in which petals replace stamens, giving double flowers, go back to ancient Greece and Rome. Similar accounts can be found in the botanical literature of China more than a thousand years ago, and in the books of the herbalists of Renaissance Europe (Meyerowitz et al., 1989). The use of such mutants (and similar but noninherited developmental abnormalities) to understand developmental processes in plants is more recent, dating from Linnaeus in the mid-eighteenth century (see Cullen and Stevens, 1990), and from Goethe (1790), who derived the ideas of organ homology and homological comparison from plants showing what was then called abnormal metamorphosis. Our term homeosis dates from Bateson's work (1894) on organismal variation, in which he expanded Masters'treatment (1889) of abnormal metamorphosis in plants to animals and introduced the term homoeosis as a replacement for the older term. Goethe (1790) used homeotic variation in plants as the basis for a specific model explaining the developmental origin of different organ types in flowers. In his view, the four types of floral organs (sepals, petals, stamens, and carpels) are all modified leaves. As sap rises through developing flowers it is progressively refined, thereby inducing different organ types in different positions.
© 1994 Cell Press. We thank G. Angenent, Ft. Coen, C. Gasser, and J. Okamura for sending us manuscripts before publication, B. Krizek, Z. Liu, J. L. Riechmann, S. Alvarez, and D. Smyth for permission to quote unpublished observations, M. Levine and E. Lewis for discussion of fly homeotic genes, and J. Chory, M. Goulding, M. Yanofsky, and members of our laboratories for critical review of the manuscript. We apologize to our colleagues whose research we did not reference because of space restrictions. Our research is supported by grants from the National Science Foundation, National Institutes of Health, United States Department of Energy, and Zeneca Seeds (E. M. M.), and also the Samuel Roberts Noble Foundation (D. W.).