Abstract
The double-flower phenotype has been selected by humans for its attractiveness in various plant species and it is of great commercial value for the ornamental market. In this study we investigated the genetic determinant of the dominant double-flower trait in carnation, petunia, and Rosa rugosa, and identified mutant alleles of TARGET OF EAT (TOE)-type genes characterized by a disruption of the miR172 target sequence and of the C-terminal portion of the encoded protein. Despite the phylogenetic distance between these eudicots, which diverged in the early Cretaceous, the orthologous genes carrying these mutations all belong to a single TOE-type subgroup, which we name as PETALOSA (PET). Homology searches allowed us to identify PET sequences in various other species. To confirm the results from naturally occurring mutations, we used CrispR-Cas9 to induce lesions within the miR172 target site of Nicotiana tabacum PET genes, and this resulted in the development of supernumerary petaloid structures. This study describes pet alleles in economically important ornamental species and provides evidence about the possibility of identifying and engineering PET genes to obtain the desirable double-flower trait in different plants.
Highlights
The variety of flower shapes and colours has fascinated humans for millennia, as witnessed by artistic depictions since ancient times
In this study we investigated the genetic determinant of the dominant double-flower trait in carnation, petunia, and Rosa rugosa, and identified mutant alleles of TARGET OF EAT (TOE)-type genes characterized by a disruption of the miR172 target sequence and of the C-terminal portion of the encoded protein
Candidate mutations for the dominant DF trait have been described in orthologous genes of the euAP2 transcription factor lineage in peach (Prunus persica) and the Rosa genus (François et al, 2018; Gattolin et al, 2018; Hibrand Saint-Oyant et al, 2018). euAP2 transcription factors are encoded by genes of the APETALA2/ETHYLENE RESPONSIVE ELEMENT-BINDING FACTOR (AP2/ ERF) family and are divided into two groups, AP2-type and TARGET OF EAT (TOE)-type, both of which are characterized by the presence of a target site for the binding of microRNA172, which negatively regulates their
Summary
The variety of flower shapes and colours has fascinated humans for millennia, as witnessed by artistic depictions since ancient times. Candidate mutations for the dominant DF trait have been described in orthologous genes of the euAP2 transcription factor lineage in peach (Prunus persica) and the Rosa genus (François et al, 2018; Gattolin et al, 2018; Hibrand Saint-Oyant et al, 2018). Wild-type Rosaceae flowers typically bear five petals In both peach and rose, mutated alleles in orthologous TOE-type genes are dominantly associated with the DF phenotype, suggesting they might act as upstream regulators of AGAMOUS (AG) and restrict its expression to the inner floral whorls (Dubois et al, 2010): such variants cause the expression of transcripts encoding truncated proteins that carry all the key functional motifs but lack the miR172 target site. Previous research has suggested that different mutations leading to the DF phenotype have occurred in the genus and were probably selected independently in R. chinensis, R. gallica, and R. rugosa (Dubois et al, 2010)
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