Brockington Group: Transcription factor evolution across independent origins of betalain pigmentation
Supervisor
Professor Sam Brockington
Importance of Research
Across the flowering plants, pigment production is controlled by one of the most conserved regulatory modules in botany: the MYB-bHLH-WD40 complex. Betalain pigmentation, which has arisen at least four times within the Caryophyllales and everywhere displaces anthocyanins, therefore poses a sharp question. Did each origin recruit the same ancestral regulator, or did each lineage solve the problem of switching on a new pathway in its own way? The fragmentary evidence available says both. In beet, the Y locus encodes an anthocyanin-like MYB that activates betalain genes; in amaranth, a related MYB has been implicated but carries an altered bHLHinteraction motif; in pitaya, the characterised regulators belong to entirely different MYB clades. If convergent phenotypes are built by non-convergent regulators, then predictability in evolution breaks down at the regulatory layer, and we need to know why.
Project Summary
This project will systematically identify and functionally compare the transcription factors controlling betalain synthesis across all four independent origins. The central hypothesis is that convergence declines up the regulatory hierarchy: structural enzymes are repeatedly co-opted from the same ancestral genes, whereas regulators are recruited opportunistically from whatever was locally available. Testing this requires that regulators are identified in lineages where none is known, that their targets and binding sites are mapped, and critically that they are exchanged between lineages to ask whether the solutions are interchangeable or lineage-specific. The loss of bHLH dependency in these MYBs is a particular focus, because it marks the moment the module was released from its ancestral partnership.
What the successful applicant will do
You will combine transcriptomic and co-expression analysis with chromatin and DNA-affinity profiling to identify candidate regulators and their cisregulatory targets in four focal species. Candidates will be validated by transient assays in Nicotiana benthamiana, by stable transformation and CRISPR knockout in Beta vulgaris and Amaranthus, and by protein interaction assays. Reciprocal swaps between origins, and ancestral sequence reconstruction of the MYB lineage, will test when and how regulatory function was gained.