Mudalige-Jayawickrama, Rasika , Kuehnle, Heidi .
Deciphering the molecular genetics of floral symmetry in Dendrobium orchid.
The Orchidaceae family is one of the largest and most diverse among flowering plants with bilateral floral symmetry (zygomorphy). Orchid flowers display a highly modified dorsal petal termed lip (labellum) unique in shape and color. In pansy-lip Dendrobium mutants, this specialized lip is replaced by a normal petal, changing the symmetry of the perianth from bilateral to radial. Recent research has revealed that floral symmetry in several eudicot plant families is determined by genes encoding TCP transcription factors similar to CYCLOIDEA and DICHOTOMA genes of Antirrhinum majus. The genetic mechanism of floral symmetry has not yet been revealed for monocot plant families. Our research is focused on a pansy-lip mutant, Dendrobium grex. Ethel Kamemoto, to characterize the gene(s) for floral symmetry in orchids. Classical breeding data of a pansy-lip x normal-lip cross determined that pansy-lip trait is due to a single, recessive, loss of function, mutation. Subtractive hybridization of cDNA from lip versus petal, and normal-lip versus pansy-lip siblings, resulted in identification and isolation of Den-TCP-1 gene that encodes a TCP transcription factor. Sequence analysis of Den-TCP-1 confirms the presence of the TCP domain and a partial R-box in the deduced amino acid sequence. Southern analyses of parents, F1, and F2 lines of D. Ethel Kamemoto hybrid have shown that the TCP gene family is represented by at least four members in each parent. The restriction patterns of TCP genes of the pansy-lip and normal-lip sibling lines from F2 segregate to resemble that of the original parental lines. Qualitative expression of Den-TCP-1 of normal-lip and pansy-lip mutant lines by RT-PCR suggests both phenotypes express the Den-TCP-1 mRNA in lips and petals despite their differences in symmetry. Quantitative expression is being studied by northern analyses to compare the levels of expression in different floral parts of the normal lip phenotype, and the flower buds of pansy-lip and normal-lip sibling lines. We will discuss the evidence in support of the independent recruitment of a TCP gene in the evolution of floral symmetry in the orchids, one of the most evolved monocot plant families with zygomorphic flowers.
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1 - University of Dubuque, Department of Natural and Applied Sciences, 2000 University Avenue, Dubuque, IA, 52001, USA
2 - University of Hawaii, Department of Tropical Plant and Soil Sciences
TCP gene family.
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM