Abstract
One of the well-known floral abnormalities in flowering plants is the double-flower phenotype, which corresponds to flowers that develop extra petals, sometimes even containing entire flowers within flowers. Because of their highly priced ornamental value, spontaneous double-flower variants have been found and selected for in a wide range of ornamental species. Previously, double flower formation in roses was associated with a restriction of AGAMOUS expression domain toward the centre of the meristem, leading to extra petals. Here, we characterized the genomic region containing the mutation associated with the switch from simple to double flowers in the rose. An APETALA2-like gene (RcAP2L), a member of the Target Of EAT-type (TOE-type) subfamily, lies within this interval. In the double flower rose, two alleles of RcAP2L are present, one of which harbours a transposable element inserted into intron 8. This insertion leads to the creation of a miR172 resistant RcAP2L variant. Analyses of the presence of this variant in a set of simple and double flower roses demonstrate a correlation between the presence of this allele and the double flower phenotype. These data suggest a role of this miR172 resistant RcAP2L variant in regulating RcAGAMOUS expression and double flower formation in Rosa sp.
Highlights
Roses are widely used as garden ornamental plants and cut flowers worldwide
To further address the correlation between the presence of the RcAP2L∆172 allele and double flower formation, we investigated its presence in the available genomic data from five other rose genotypes that exhibit either double flowers (R. odorata ‘Hume’s Blush’, R. x hybrida ‘La France’) or simple flowers (R. chinensis ‘Sanguinea’, R. chinensis ‘Spontanea’ and R. wichurana)[27]
RcAG does not lie within the double flower interval suggesting that a yet unknown upstream regulator of RcAG must be the determinant of double flower formation
Summary
Roses are widely used as garden ornamental plants and cut flowers worldwide. A number of their agricultural and decorative traits specify their commercial value[1] and have been selected during domestication. Double flower refers to a characteristic of modern roses giving blooms with an increased number of petals that can vary from 10 to more than 200 petals per flower, whereas wild-type simple flowers are composed of 5 petals This characteristic is tightly associated with flower development and organ identity patterning, as it results from homeotic conversion of stamens into petals[3]. In Petunia, the restriction of the C-class gene expression needs mainly the actions of the microRNA BLIND, but involves a gene from the euAP2 family, PhBEN11,12 This diversity of the canonical ABCE functions, together with the absence of comprehensive genome data giving access to all members of each gene family, hampered the identification of the key genes determining floral organ identity in non-model species, such as in rose. The data provide a basis for a mechanism by which double flowers are formed and open new perspectives to dissect in detail the underlying molecular and biochemical mechanisms in roses and likely in other species
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