As sessile organisms, plants have evolved a diverse array of specialized metabolites to respond to their environments. Specialised metabolites are frequently restricted to particular plant lineages, such as the specialised betalain pigments, which are unique to the flowering plant order Caryophyllales - betalains will be familiar as the colour of beetroot. However there are also striking examples of convergent evolution, with the same specialized metabolites emerging independently in different lineages. The host laboratory has recently shown that the betalain biosynthesis pathway has evolved multiple times within Caryophyllales. Underpinning four convergent origins of betalain pigmentation, the central enzyme in the betalain pathway, 4,5-DOPA-extradiol -dioxygenase (DODA), has evolved four times via gene duplication and neofunctionalization. Preliminary data indicate that DODA enzymes from different origins have distinct kinetic profiles, of significance to biotechnology. In the proposed research, I will elucidate the molecular basis underlying the repeated evolution of L-DOPA dioxygenase activity, and resolve the molecular evolutionary trajectories underlying different enzymatic catalytic profiles across different origins of betalain synthesis. Convergent evolution provides a natural experiment in understanding the genetic basis of repeated emergence and optimization of a metabolic pathway. In exploring the molecular basis of the convergent evolution of high DODA activity, I expect to address many central questions in evolutionary biology, including the respective roles of parallel evolution, epistasis, adaptive constraint, and contingency, in the evolution of molecular complexity.
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