Brockington Group: Replaying the tape: what four origins of betalain pigmentation reveal about convergent evolution
Supervisor
Professor Sam Brockington
Importance of Research
Convergent evolution is biology's closest approach to a repeated experiment. When the same complex trait arises independently in different lineages, we can ask whether evolution reaches the same solution by the same genetic route, and therefore whether the outcomes of evolution are in any sense predictable. Betalain pigmentation is an exceptional system for this question. These pigments have arisen at least four times within the Caryophyllales, they replace the anthocyanins found almost everywhere else in flowering plants, and remarkably the two pigment classes are never found together in the same plant. That mutual exclusivity implies that pigment replacement involves coordinated change across a whole regulatory network, not a single switch, and makes betalains a rare opportunity to read out a genetic rulebook for the repeated evolution of complex traits.
Project Summary
This project tests the hypothesis that each independent origin of betalain pigmentation involved a convergent suite of genetic changes across multiple components of a network: novel enzymes, co-opted enzymes, transcriptional regulators and the loss or silencing of the anthocyanin pathway. By reconstructing the network in four species representing four separate origins, you will determine how much of the solution is repeated, how much is idiosyncratic, and which components are constrained. You will also address the long-standing puzzle of why anthocyanins and betalains are mutually exclusive, testing whether the answer is regulatory interference, metabolic competition or ecological selection.
What the successful applicant will do
You will reconstruct gene regulatory networks in four focal species using transcriptomic, phylogenomic and comparative genomic approaches, and quantify the extent to which components were repurposed from the ancestral anthocyanin pathway. You will use stable and transient transformation, heterologous assays and synthetic biology to test the function and interchangeability of components across origins, including reciprocal swaps between lineages. Comparative analysis across all four origins will establish whether convergence follows consistent genetic rules.