The Genetic Basis of Floral Organ Identity and Its Applications in Ornamental Plant Breeding

Chapter 2Petunia hybrida (or garden petunia) is worldwide one of the most popular bedding plants. At the same time, petunia has a decades-long history as a model species for scientific research to study a variety of processes, including floral organ development. Here we explain the genetic basis of floral organ identity in a comprehensible manner and illustrate the potential of floral organ identity mutants for ornamental plant breeding, using petunia as an example. Although the B-and C-floral organ identity functions are well conserved at the molecular level, indicating broad applicability, different species may exhibit significant differences in the degree of redundancy versus subfunctionalization/ specialization among duplicated pairs of the homeotic genes. This is a direct consequence of the complex origin of different plant genomes, which were shaped by whole-genome, large and small-scale duplication events, often leading to (partial) genetic redundancy. Since classical genetic screens only can uncover nonredundant functions, this is probably the main reason why the use of floral organ identity mutants as breeding targets has remained unexplored in many ornamentals. We discuss how different breeding strategies may cope with this phenomenon