Flower symmetry evolution: towards understanding the abominable mystery of angiosperm radiation

Abstract

Flower symmetry is considered a morphological novelty that contributed significantly to the rapid radiation of the angiosperms, which already puzzled Charles Darwin and prompted him to name this phenomenon an `abominable mystery'. In 2009, the bicentenary of Darwin's birth and the 150th anniversary of the publication of his seminal work, `On the Origin of Species', this question can now be more satisfactorily readdressed. Understanding the molecular control of monosymmetry formation in the model species Antirrhinum opened the path for comparative studies with non-model species revealing modifications of this trait. TCP transcription factors, named after TEOSINTE BRANCHED 1 in maize, CYCLOIDEA in snapdragon and PCF in rice, control flower monosymmetry development and contributed to establishing this trait several times independently in higher angiosperms. The joint advances in evolutionary and developmental plant research, combined in the novel research field named Evo/Devo, aim at elucidating the molecular mechanisms and strategies to unravel the mystery of how this diversity has been generated.