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CAPSEVO Report Summary

Project ID: 260455
Funded under: FP7-IDEAS-ERC
Country: Germany

Final Report Summary - CAPSEVO (Evolution of flower morphology: the selfing syndrome in Capsella)

The transition from animal-mediated outbreeding to selfing is one of the most frequent evolutionary changes in flowering plants. In many cases, it is accompanied by a characteristic suite of morphological and functional changes to the flowers, collectively termed the selfing-syndrome. This includes a dramatic reduction in petal size and in the amount of emitted floral scent. Despite its frequent occurrence, the genetic basis of the evolution of the selfing syndrome is very poorly understood. Therefore, we have used the model genus Capsella (Shepherd’s Purse) to unravel the genetic and molecular basis of selfing-syndrome evolution. In this genus, the ancestral outbreeding species is represented by Capsella grandiflora, from which the selfing species C. rubella was derived less than 100,000 years ago. By genetic mapping, we have identified mutations in three different genes that have contributed to the reduction in petal size, and one responsible for the loss of a major scent compound. The three petal size-related genes encode a protein that stimulates growth by degrading growth-repressors; an enzyme involved in the biosynthesis of a plant growth hormone; and a transcriptional regulator that switches off the expression of growth-inhibitory genes. Population-genetic analysis has indicated that in one of the cases the mutations leading to smaller petals were already present in the outbreeding population and have been captured by the selfing species, whereas for the second gene the mutations only arose in the selfing species after the transition to selfing. Regarding the loss of floral scent, a key enzyme required for synthesizing a prominent group of scent compounds has been inactivated in the selfing species by novel mutations.
Thus, together these results have shed light on the kinds of genes and the evolutionary history of the mutations underlying the evolution of the selfing syndrome. They provide a unique basis to address the question of how evolution repeats itself, i.e. whether the same genes have been affected in other instances of selfing-syndrome evolution, or whether there are many different ways of turning large, scented and attractive flowers into small, non-scented inconspicuous ones.

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