While eudicots have sepals in the first whorls of their flowers and petals only in the second floral whorl, lilies and tulips develop petaloid tepals in both outer floral whorls. A plausible model suggests that, while eudicots express the floral homeotic functions A and A+B in whorls one and two, respectively, members of the lily family express floral homeotic functions A+B in both whorls of the perianth. By cloning DEFICIENS- and GLOBOSA-like genes from lily and tulip, studying the expression of theses genes in wild-type and homeotically transformed flowers, and by expressing these genes in Arabidopsis we obtained preliminary evidence that the petaloid character of the first whorl organs of the Liliaceae is indeed due to the "ectopic" expression of B class floral homeotic genes in the organs of the first floral whorl. It seems likely, therefore, that changes in the expression of floral homeotic genes have played an important role in the structural diversification of the flower during the radiation of angiosperms. To further test this hypothesis we are currently studying DEF- and GLO-like genes in modified class B-type mutants (termed 'Viridiflora' varieties) that have partiallymore or less leaf-like tepals and carpelloid stamens. Moreover, we are busy cloning the AG-like gene from tulip and studying class C-type mutants of tulip with filled flowers composed of petaloid tepals (lacking stamens or carpels). These investigations will provide us with information concerning both the conservation and variation of class B and class C floral homeotic genes between core eudicots and lily-like monocots.
| Contact: | Guenter Theissen |
Suggested Reading:
Kanno, A., Saeki, H., Kameya, T., Saedler, H. and Theissen, G. (2003). Heterotopic expression of class B floral homeotic genes supports a modified ABC model for tulip (Tulipa gesneriana). Plant Mol. Biol. 52, 831-841.
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