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Chanderbali, Andre [1].

Perianth Evolution in Lauraceae.

The floral perianth of Lauraceae typically consists of two whorls of morphologically indistinguishable tepals. Although there is appreciable variation in size, texture, vestiture, and color among family members, tepal morphology is usually matched in both whorls. One frequent exception is a marked reduction in the size of the outer tepals. The resulting bipartite perianth can be witnessed in several extant genera, including Caryodaphnopsis, Persea, and Alseodaphne, and in Mauldinia of the Mid-Cretaceous. In order to determine whether orthologues of the A, B, and C-class MADS-box genes that determine floral organ identity in eudicot angiosperms have played a role in shaping the bipartite perianth in Lauraceae, relative quantitative RT-PCR was used to assess their expression levels in the reduced outer tepals of Persea borbonia relative to the normal outer tepals of Persea americana. The results indicate that the Persea orthologues of genes with A- and B-class function are expressed at comparable levels in the two species, but that of C-class genes has withdrawn from the outer tepals of P. borbonia. These findings imply that normal development of the perianth organs in Lauraceae requires C-class gene expression. Furthermore, preliminary developmental observations indicate that the bipartite perianth in P. borbonia results from failure of the outer tepal whorl to develop fully. During the later stages of floral development the inner tepals experience a rapid increase in size, apparently in synchrony with stamen elongation, but the outer tepals remain in an unexpanded state. These observations tempt speculation that C-class genes in Persea facilitate the coordination of floral organ development. According to this interpretation the withdrawal of C-class gene expression from the outer tepals of P. borbonia has uncoupled these organs from the developmental program of the inner floral whorls. In the bipartite lauraceous perianth therefore, the outer tepals may represent an arrested developmental condition.

1 - Florida Museum of Natural History, University of Florida, Gainesville, Florida, 32611-7800, USA

Keywords:
perianth
ABC model
Persea
Lauraceae
MADS-box genes.

Presentation Type: Poster
Session: 32-151
Location: Special Event Center (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 12:30 PM
Abstract ID:1013