Genetic architecture and evolution of the S locus supergene in Primula vulgaris

Jinhong Li, Jonathan M. Cocker, Jonathan Wright, Margaret A. Webster, Mark McMullan, Sarah Dyer, David Swarbreck, Mario Caccamo, Cock van Oosterhout, Philip M. Gilmartin

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Abstract

Darwin’s studies on heterostyly in Primula described two floral morphs, pin and thrum, with reciprocal anther and stigma heights that promote insect-mediated cross-pollination. This key innovation evolved independently in several angiosperm families. Subsequent studies on heterostyly in Primula contributed to the foundation of modern genetic theory and the neo-Darwinian synthesis. The established genetic model for Primula heterostyly involves a diallelic S locus comprising several genes, with rare recombination events that result in self-fertile homostyle flowers with anthers and stigma at the same height. Here we reveal the S locus supergene as a tightly-linked cluster of thrum-specific genes that are absent in pins. We show that thrums are hemizygous not heterozygous for the S locus, which suggests that homostyles do not arise by recombination between S locus haplotypes as previously proposed. Duplication of a floral homeotic gene 51.7 MYA, followed by its neofunctionalisation, created the current S locus assemblage which led to floral heteromorphy in Primula. Our findings provide new insights into the structure, function and evolution of this archetypal supergene.
Original languageEnglish
Article number16188
JournalNature Plants
Volume2
DOIs
Publication statusPublished - 2 Dec 2016

Keywords

  • Primula
  • S locus
  • heterostyly

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