Flavonoid diversification in Hibiscus and its impact on petal pattern evolution

Flowers are a key evolutionary innovation in plants, facilitating animal-mediated pollination through distinct pigmentation patterns on their petals. While their ecological significance is known, the developmental and evolutionary origins of these patterns remain less understood. In Hibiscus trionum, a new model system, bullseye patterns are formed by flavonoid pigments including anthocyanins and flavonols. Their flowers display a contrast between a purple base and an off-white distal region. H. trionum belongs to the Trionum Complex native to Australia and New Zealand, whose members vary in bullseye size and colour. This thesis investigates the genetic basis of bullseye patterning and flavonoid pathway diversification across the complex, linking molecular changes to pigment diversity. Flavonoid biosynthesis is regulated by MBW complexes comprising MYB (myeloblastosis) and bHLH (basic helix-loop-helix) transcription factors and a WD40 co-factor. I identified a gene regulatory network centred on the R2R3 MYB HtBERRY1 to regulate anthocyanin biosynthesis at the petal base of H. trionum. Within the Trionum Complex, bullseye loss is observed in multiple species. In H. richardsonii and two H. verdcourtii populations, I found that changes in HtBERRY1 activity were related to the reduced bullseye trait. This demonstrated an example of replicated/convergent evolution whereby a single locus, BERRY1, was implicated in bullseye loss across multiple independent lineages of the Trionum Complex. To complement this genetic investigation, I analyzed flavonoid profiles using HPLC-MS/MS and uncovered inter- and intraspecific variation in pigment composition. H. verdcourtii produced unique flavonols and anthocyanins, suggesting shifts in the flavonoid pathway caused by differences in key biosynthetic genes. In the final part of this work, I further explore the role of BERRY1 and alternative factors underpinning the regulation of flavonoid biosynthesis. I identified interacting bHLH partners and investigated upstream regulators using candidate gene and non-targeted approaches. Manipulating the TEOSINTE BRANCHED 4 (TCP4) transcription factor affected bullseye size by altering petal growth. Comparative genetics with another H. trionum accession further verified interactions between components of the gene regulatory network and may uncover additional BERRY1 regulators. Together, this work integrates genetic, chemical, and phylogenetic approaches to reveal how evolution of the flavonoid pathway shapes floral pigmentation. These findings advance our understanding of petal patterning in angiosperms.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Yeo, May Thin Soe

Advisor dc:contributor.advisor

• Moyroud, Edwige

• evolution
• development
• plant biology
• petal patterning
• molecular biology
• phylogenetics
• genetics

Licence

• https://www.repository.cam.ac.uk/bitstreams/f1bb6077-55ed-4d1e-a2e7-a4e67caf69b6/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.123481

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/392955