Mechanisms underlying morphological diversity in plants

Mating system shifts recurrently drive specific changes in organ morphology. The shift in mating system from outbreeding to selfing is one of the most frequent evolutionary transitions in flowering plants and is often associated with a set of characteristic changes in flower morphology and function termed “the selfing syndrome”. Predominantly selfing species often have much smaller flowers than their outbreeding relatives. They also show a reduced pollen-to-ovule ratio, usually due to a lower pollen production, and produce less nectar and scent. Yet, the evolutionary paths along which such polygenic traits evolve are poorly understood.

The genus Capsella in the Brassicaceae family has emerged as an ideal model to address the genetics of morphological evolution after the transition to selfing. The transition to selfing has occurred independently twice in this genus, and in both cases, this has been followed by a strong reduction of flower size. We used this genus to investigate the genetic and developmental basis of the convergent evolution of flower morphology after the transition to selfing. Our findings started to unravel the evolutionary and molecular mechanisms underlying the evolution of selfing syndrome traits. The results presented here highlight how the additive effects of segregating variants may contribute to the rapid evolution of polygenic traits and emphasize the importance of a modular gene regulatory architecture for enabling organ-specific morphological evolution.