Abstract Detail

Development and Structure

Martínez-Salazar, Sebastián [1], Kramer, Elena [2], Gonzalez, Favio [3], Pabon Mora, Natalia [4].

Molecular mechanisms controlling nectar spur development in nasturtiums (Tropaeolaceae).

The monogeneric Tropaeolaceae (Brassicales) comprises ca. 100 species native to South and Central America. Tropaeolaceae flowers have a floral tube derived from the fused proximal region of perianth whorls. Late in flower development, the adaxial region of this floral tube expands and evaginates forming a nectar spur, which constitutes a synapomorphy of the family. In this study, we used a candidate gene approach to identify genes responsible for nectar spur development in Tropaeolaceae. Our list of candidate genes comprised CYCLOIDEA, CINCINNATA, RADIALIS, DIVARICATA, POPOVICH and class I KNOX genes. The candidate gene that we found to be expressed concomitantly with spur initiation and elaboration is a CINCINNATA (CIN) homolog. We reconstructed the evolution of the CIN gene lineage and found several duplications in core eudicots with one of the resulting clades corresponding to TCP3/4L. Based on transcriptomic data, we found that Tropaeolaceae possess two TCP3/4L copies, as a result of a Tropaeolum-specific gene duplication. These two copies (TCP4L1 and TCP4L2) in T. longifolium show overlapping expression in epidermal cell layers of reproductive apices and young floral buds, but only TlTCP4L2 shows differential expression in the floral tube at early stages of nectar spur formation, restricted to the adaxial region. This adaxial expression of TlTCP4L2 overlaps with the expression of cell division markers. Later in development, both TlTCP4L copies are expressed in the secretory tissue of the spur. Based on these results, we hypothesize that Tropaeolaceae TCP4L genes had a plesiomorphic role in epidermal specializations and nectary development and that, after gene duplication, TCP4L2 acquired a new function in nectar spur initiation and growth by promoting cell division. To better understand nectar spur evolution in Tropaeolaceae, it is critical to expand developmental genetic studies to their sister group (Akaniaceae). Akaniaceae lack the duplication of TCP4L genes and have flowers that develop a floral tube without nectar spurs.

1 - Universidad De Antioquia, Instituto De Biología, Calle 70 #52-21, Medellín, ANT, 050010, Colombia
2 - Harvard Univ., OEB, 16 Divinity Avenue, BL 1119, Cambridge, MA, 02138, United States
3 - Universidad Nacional de Colombia, Sede Bogotá, Facultad de Ciencias, AA 7495, Bogotá, Colombia
4 - Universidad De Antioquia, Ciudad Universitaria, Aa1226, Medellin, ANT, 050010, Colombia

Keywords:
Floral Symmetry
Brassicales
CINCINNATA
Evo-Devo
floral tube
Tropaeolum
nectar spur development.

Presentation Type: Oral Paper
Number: DS1007
Abstract ID:622
Candidate for Awards:Katherine Esau Award,Maynard F. Moseley Award,Developmental and Structural Section Graduate Student Registration Award