Under the rainbow: Novel insights on the mechanisms driving the development and evolution of petal pigmentation

Flower colours have intrigued scientists and artists alike across the ages, but our understanding of how flowers paint their corolla is largely incomplete. Here, we explore how recent studies are bringing to light the dark side of flower colour. We review novel discoveries related to the molecular mechanisms underpinning petal pigmentation, and we argue that colour patterns on the corolla constitute powerful experimental systems to address complex biological questions, including the outcomes of gene duplication, the emergence of novelty, and the significance of regulatory and coding changes in generating morphological diversity. Natural variants represent fantastic resources not only to discover the genetic basis of biodiversity, but also to fill gaps in our understanding of the processes plants employ to appear colourful. As modifications of pigment production often yield striking, tractable phenotypes, floral colour studies provide unique opportunities to illuminate key developmental questions associated with morphogenesis and patterning. Exploring petal pattern variation in an ever-increasing range of species uncovers new research avenues to comprehend the inner workings of development and evolution. By understanding these processes, we are better equipped to program plant behaviour to enhance floral traits and to gain unprecedented insights into the strategies that shape speciation and the emergence of Darwin's 'endless forms most beautiful and most wonderful'.