报告题目：Genetic architecture and evolution of the S locus supergene in Primula vulgaris
报 告 人: Professor Phillip Gilmartin, Dean of the Faculty of Science，University of East Anglia
报告时间: 3月29日 10:00-11:00
Charles Darwin’s observations on the two forms of flower in Primula, known as pin and thrum, identified heterostyly as a breeding system that enhances cross-pollination. Pin flowers have a long style and low anthers that produce small pollen, thrum flowers have a short style and high anthers that produce large pollen. The reciprocal position of male and female reproductive structures in the two forms of flower facilitates insect-mediated cross-pollination; a self-incompatibility (SI) system also reduces self-pollination. Plants produce only pin or only thrum flowers. Development of the two forms of flower and the SI system are controlled by a cluster of genes known as the S (Style length) locus. The thrum form is dominant over the pin form; thrums behave as heterozygotes and pins as homozygous recessives with a 50:50 ratio of pin:thrum plants in a population. Rare homostyle individuals with the anthers and stigma at the same height in self-fertile flowers occur and these were assumed to be the result of recombination between dominant and recessive S alleles. We recently completed the genome sequence of P. vulgaris and identified and characterised the S locus gene cluster. This cluster contains five genes, one controls anther elevation, another reduces style length in thrum flowers. Our recent findings provide new insight into the origin and maintenance of heterostyly. Thrum plants are not heterozygous as predicted but are hemizygous; there is no pin allele, the five S locus genes are absent from the pin genotype. The hemizygous nature of the S locus means that homostyles cannot occur by recombination as presumed; instead, they arise though mutation of S locus genes. We dated the duplication origin of one S locus gene to 51.7M years ago, before speciation of the ~430 Primula species; we therefore predict that heterostyly arose only once in the Primulaceae.