Identification and molecular characterization of the DOMINANT DOUBLE (DODO) and DOUBLE FLOWER (DF) mutations in Petunia and Rose – DODO

To precisely locate the mutations on the Rosa and Petunia chromosomes, a genetic mapping approach was undertaken. It is combined with a large scale analysis of genes (DNA), and of transcripts (RNA). The combined data should generate a list of interesting candidate genes which will be tested in planta.

The project is starting, so little information is available for outreach. However, we already know that the genetic mapping approach led to the identification of chromosome portions in Rosa and in Petunia, which contain the mutated locus. Gene content around this locus is currently being analyzed.

This data will certainly allow to gain knowledge of flower development for both species.

No publication or patents are available for now.

Identification and molecular characterization of the DOMINANT DOUBLE (DODO) and DOUBLE FLOWER (DF) mutations in Petunia and Rose.

Unraveling the control and evolution of flower development is of fundamental interest for plant biology. During the past two decades, enormous progress has been made in the understanding of how floral organ identity and architecture are controlled at the genetic and molecular level. Most of this research has been conducted in the model plant Arabidopsis thaliana. Especially the cloning of the floral mutants underlying the famous ABC(E) model has served as a framework to understand evolution of the flower and flower development in other species. The best known floral abnormality is the “double-flowered” characteristic, which groups all varieties of flowers that develop extra petals, sometimes even containing entire flowers within flowers. Because of their highly priced ornamental value, double flowered varieties have been found and selected for in a wide range of ornamental species. In Arabidopsis, the double flowered recessive agamous (ag) mutant was cloned and turned out to encode a MADS-box transcription factor. AG represents the C-function gene in the ABC model, and is required for stamen and carpel identity. Typically in C-function mutants, stamens are replaced by petals while a new aberrant flower reiterates in the flower center. While a recessive C-function gene mutation might indeed account for double flower phenotypes in some species, many double flowered varieties are genetically dominant, and their phenotype cannot simply be explained by a defective C-function gene. For example, in Rose the double flower phenotype is associated with a dominant mutation in the yet unknown DF (DOUBLE FLOWER) locus, which leads to a boundary shift of AG toward the center of the flower, where stamens and pistils still develop normally. Similarly in Petunia DODO (DOminant DOuble) flowers, stamens and a pistil still can develop, despite the presence of petals in the inside of the flower, while stamen number usually is also increased. In addition, petal number is increased also in the 2nd whorl, which falls outside the C -expression domain.. The molecular basis that underlies these dominant double flower phenotypes has remained completely elusive to date. The molecular identification of dominant double flower mutations is therefore of fundamental interest, and would represent another major breakthrough in our understanding of flower architecture and evolution. With this project, we aim to identify the molecular basis of dominant double flower formation in Petunia and Rose, two major ornamental species in which the selection of dominant double flower varieties have played a crucial role during their domestication and commercialization. Exploiting our expertise in these two species, we propose to use a parallel mapping strategy to accomplish this goal. Because the dominant double flower phenotypes in Petunia and Rose are very similar, we believe that there is a strong possibility that they are affected in the same locus. If so, this will greatly accelerate the mutation’s identification. Via a genome-wide digital gene expression (DGE) analysis, we will create a global overview of the developmental processes affected in dominant double flowers. In case the DODO and DF phenotypes would be caused by an epigenetic mechanism or by a mutation in a regulatory sequence, this DGE analysis will also be helpful to identify the DF and DODO loci by mapping differentially expressed transcripts within the mapping intervals. The ‘in house’ available large collection of floral homeotic mutants in Petunia in addition will allow a genetic characterization and positioning of the dominant double flower mutation within the ABC framework. Finally, functional studies and analyses of the diversity of double flower mutations will validate the initial steps of the mutation identification.