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Title: The genomic and evolutionary analysis of floral heteromorphy in Primula
Author: Cocker, Jonathan
ISNI:       0000 0004 7227 0878
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2016
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The genetic basis and evolutionary significance of floral heteromorphy in Primula has been debated for over 150 years. Charles Darwin was the first to explain the importance of the two heterostylous floral morphs, pin and thrum, suggesting that their reciprocal anther and stigma heights facilitate cross-pollination, and showing that only between morph crosses are fully compatible. This key innovation is an archetypal example of convergent evolution that serves to physically promote insect-mediated outcrossing, having evolved in over 28 angiosperm families . Darwin’s findings laid the foundation for an extensive number of studies into heterostyly that contributed to the establishment of modern genetic theory. The widely accepted genetic model portrays the Primula S locus, which controls heterostyly and self-incompatibility, as a coadapted group of tightly-linked genes, or supergene. It is predicted that self-fertile homostyle flowers, with anthers and stigma at the same height, arise via rare recombination events between dominant and recessive alleles in heterozygous thrums. These observations have underpinned over 60 years of research into the genetics and evolution of heterostyly. The Primula vulgaris genome assembly and associated transcriptomic and comparative sequence analyses have facilitated the assembly and characterisation of the complete S locus in this species. Here it is revealed that thrums are hemizygous not heterozygous: the S locus contains five thrum-specific genes which are completely absent in pins, which means recombination cannot be the cause of homostyles as previously believed. The studies also reveal candidate genes in Primula veris and other species, and have facilitated an estimation for the assembly of the S locus supergene at 51.7 MYA. These findings challenge established theory, and reveal novel insight into the structure and origin of the Primula S locus, providing the foundation for understanding the evolution and breakdown of insect-mediated outcrossing in Primula and other heterostylous species.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available