Plant & Animal Genomes XIII Conference

January 15-19, 2005
Town & Country Convention Center
San Diego, CA

ABCs Of Basal Angiosperms: Expression Profiles Of Floral Organ Identity Genes In Amborella (Amborellaceae), Nuphar (Nymphaeaceae), Illicium (Austrobaileyales), And Some Magnoliids

Sangtae Kim¹ , Jin Koh¹ , Mi-Jeong Yoo¹ , Hongzhi Kong² , Yi Hu² , Hong Ma² , Pamela S. Soltis³ , Douglas E. Soltis¹

¹  Department of Botany, University of Florida, Gainesville, FL 32611, USA

²  Department of Biology and the Huck Institute of Life Sciences, Pennsylvenia State University, University Park, PN 16802, USA

³  Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA

The ABC model was established based on functional studies of floral organ identity genes of Arabidopsis and Antirrhinum, both of which are highly derived eudicots. However, most of the diversity in arrangement and number of floral parts is found among basal angiosperm lineages which constitute only a small percentage of extant species. To address the broad applicability of the ABC model, we isolated and investigated the expression patterns of A, B, and C-function genes in the basal angiosperms Amborella (Amborellaceae), Nuphar (Nymphaeaceae), Illicium (Austrobaileyales), and representatives of the magnoliid clade. We used relative quantitative RT-PCR, in situ hybridization studies, and real-time PCR. Gene expression patterns in basal angiosperms differ from those in eudicots and monocots in several ways: 1) genes of the AP1 family (A class) were generally expressed in the fourth whorl (carpels) of flowers and in leaves, but expression was absent or weak in the first and second whorls, 2) genes of the AP3/PI family (B class) were generally expressed in the first and fourth whorls, in addition to the second and third whorls, 3) genes of the AG family (C class) were expressed in stamens and carpels in all species, and also in tepals of Illicium. Floral organ identity genes in basal angiosperms show a broader range of expression across floral whorls than in eudicots and monocots, consistent with gradual morphological transitions between adjacent floral organs. The data suggest that floral organ identity genes acquired specialized function after the early diversification of flowering plants.