Lead supervisor: Samuel Brockington, Plant Sciences
Co-supervisor: Nicola Patron, Plant Sciences
Brief summary:
You will work on one of the great enduring mysteries of plant evolution: how and why betalain pigmentation evolved to replace canonical anthocyanin pigmentation.
Importance of the area of research concerned:
As sessile organisms, plants have evolved a diverse array of specialized metabolites to adapt to their environments. Specialized metabolites are frequently restricted to particular plant lineages, but can show striking examples of convergent evolution, with the same specialized metabolites emerging independently in different lineages. For example, we have recently shown that the betalain biosynthesis pathway has evolved multiple times, underpinning four convergent origins of betalain pigmentation. Betalains are an unusual class of pigments, that are best known as the colour of beetroot, and are unique to the flowering plant order Caryophyllales. In betalain-pigmented species, the betalain replace the more common plant pigments, called anthocyanins. Anthocyanins and betalains have never been found to co-occur in nature, but the mechanisms for this is unknown. Convergent evolution provides a natural experiment in the repeated emergence and optimization of a genetic pathway. In examining the convergent evolution of betalain biosynthesis, we expect to uncover a common set of rules that explain how a complex trait such as betalain pigmentation can repeatedly evolve.
Project summary :
The long-term goal of our research group is to resolve the step wise evolutionary emergence of a complex specialized metabolic trait. The objective of this PhD is to build on our recent discovery that betalain pigments have convergently evolved at least four times in Caryophyllales. Our central hypothesis is that, each independent origin of the betalain metabolic pathway will have entailed a convergent suite of associated genetic change across multiple genetic components. You will use exceptional phylogenomic resources for Caryophyllales and proven heterologous assays to assess the evolution of key genes and gene networks involved in the betalain biosynthesis pathway. Using the combined power of these tools, you will resolve major steps in the evolution of the betalain pathway and explore how and why it has evolutionarily replaced the analogous pigments, anthocyanins.
What will the student do?:
You will construct genetic networks in four species, representing each evolutionary origin of the betalin pigmentation pathway. Using phylogenetic, transcriptomics, and phylogenomics you would explore how these genetic networks were assembled and determine to what extent the genetic toolkit was "stolen" from the competing anthocyanin pigment pathway. You will use various established wet-lab techniques using heterologous genetic transformation, and synthetic biology approaches to understand the evolution, neofunctionalization and adaptation of key genes in this network. You will compare and contrast the emerging genetic networks for each origin of betalain pigmentation to determine to what extent they follow the same evolutionary trajectories, and to what extent the rules of convergent evolution are genetically hard wired. You will then explore the basis of the mutual exclusion of the two pigment types and test a number of hypotheses to explain why the two pigment cannot co-occur using a combination of wet and dry lab approaches.
References - references should provide further reading about the project:
Brockington, S.F., Walker, R.H., Glover, B.J., Soltis, P.S. and Soltis, D.E. (2011) Complex Evolution of Pigmentation in the Caryophyllales. New Phytologist 190: 854–864. doi:10.1111/j.1469-8137.2011.03687.x
Sheehan, H., et al. (2019) Evolution of L‐DOPA 4,5‐Dioxygenase Activity Allows for Recurrent Specialisation to Betalain Pigmentation in Caryophyllales. New Phytologist 227(3): 914 - 929. doi:10.1111/nph.16089
Brockington, S.F., et al. (2015) Lineage-specific Gene Radiations Underlie the Evolution of Novel Betalain Pigmentation in Caryophyllales. New Phytologist 207(4): 1170-1180. doi:10.1111/nph.13441
Applying
You can find out about applying for this project on the Department of Plant Sciences page.