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How to spot a daisy (evolution and development of petal spots)

Supervisor: Beverley Glover (Plant Sciences)

glover 1

Project outline:

This project aims to understand the evolution and development of dark petal spots on flowers, particularly of the daisy family, as a model for understanding flower diversity more generally. Many flowers in the daisy family produce dark spots on the petals of some or all of their ray florets. These spots may be very simple patches of pigment, or more complicated 3-dimensional structures. Gorteria diffusa produces raised dark spots at the base of some (usually 1–3) ray florets. Pollination studies have demonstrated that these structures are mimics of small bee-flies (Megapalpus capensis) that are attracted to the petal spots and show an aggregating, feeding or mating response. Although many petal spots are primarily an accumulation of pigments, those of Gorteria are relatively complex, consisting of three different cell types and localized, very concentrated anthocyanin deposition. In the centre of the spot is a white highlight patch, containing no anthocyanin, and around the highlight are interior cells with high concentrations of anthocyanin and chlorophyll pigments. In a horseshoe-shape around the entire spot are large papillae, which contain the greatest concentration of anthocyanin and give the spot its three-dimensional appearance.

In this project you will consider the development of the complex insect-mimicking spot of Gorteria diffusa and the evolution of this developmental programme, by taking 3 approaches which bring different training opportunities:

  1. We have identified the transcriptional regulator that activates anthocyanin synthesis in the petal spots. Its expression pattern is spatially restricted to the spot region. Therefore, by identifying the transcriptional regulators that activate its expression, we can now isolate the master genes controlling spot identity. TRAINING: yeast 1-hybrid analyses to identify candidate regulators, expression analysis using qRT-PCR, transgenic approaches.
  2. Gorteria diffusa contains at least 12 variants, differing greatly in spot characteristics. These “morphotypes” are found as semi-discrete populations within the narrow endemic range Gorteria occupies in the Northern Cape district of South Africa. The petal spots of the different morphotypes vary in number on the capitulum; number of white highlights within the spot; extent and position of the papillae; and amount of anthocyanin. We will study how the petal spot genes function in each of these morphotypes. TRAINING: expression analyses, transgenic approaches, handling genotyping-by-sequencing data.
  3. Many closely related daisies found in the same habitat also produce petal spots, although of a much simpler type. You will explore the evolution of these in a phylogenetic context by assessing whether the Gorteria petal spot genes play a role in spot development in other species. TRAINING: cloning from non-model systems, phylogeny reconstruction.

References:

  • Thomas, M., Rudall, P., Ellis, A., Savolainen, V. & Glover, B.J. (2009) Development of a complex floral trait: the pollinator-attracting petal spots of the beetle daisy, Gorteria diffusa (Asteraceae). American Journal of Botany 96, 2184-2196.
  • Ellis, A., Brockington, S., de Jager, M., Mellers, G., Walker, R. & Glover, B.J. (2014) Floral trait variation and integration as a function of sexual deception in Gorteria diffusa. Philosophical Transactions of the Royal Society Series B 369, 20130563.