Abstract
BackgroundThe R2R3-MYB genes regulate pigmentation and morphogenesis of flowers, including flower and cell shape, and therefore have importance in the development of new varieties of orchids. However, new variety development is limited by the long breeding time required in orchids. In this study, we identified a cDNA, DhMYB1, that is expressed during flower development in a hybrid orchid, Dendrobium hybrida (Dendrobium bobby messina X Dendrobium chao phraya) then used the direct application of dsRNA to observe the effect of gene silencing on flower phenotype and floral epidermal cell shape.ResultsFlower bud development in the Dendrobium hybrid was characterised into seven stages and the time of meiosis was determined as between stages 3 to 5 when the bud is approximately half of the mature size. Scanning electron microscopy characterisation of adaxial epidermal cells of the flower perianth, showed that the petals and sepals each are divided into two distinct domains based on cell shape and size, while the labellum comprises seven domains. Thirty-two partial cDNA fragments representing R2R3-MYB gene sequences were isolated from D. hybrida. Phylogenetic analysis revealed that nine of the translated sequences were clustered with MYB sequences that are known to be involved in cell shape development and from these, DhMYB1 was selected for full length cDNA cloning and functional study. Direct application of a 430 bp dsRNA from the 3’ region of DhMYB1 to emerging orchid flower buds reduced expression of DhMYB1 RNA compared with untreated control. Scanning electron microscopy of adaxial epidermal cells within domain one of the labellum of flowers treated with DhMYB1 dsRNA showed flattened epidermal cells whilst those of control flowers were conical.ConclusionsDhMYB1 is expressed throughout flower bud development and is involved in the development of the conical cell shape of the epidermal cells of the Dendrobium hybrida flower labellum. The direct application of dsRNA changed the phenotype of floral cells, thus, this technique may have application in floriculture biotechnology.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0577-3) contains supplementary material, which is available to authorized users.
Highlights
The R2R3-MYB genes regulate pigmentation and morphogenesis of flowers, including flower and cell shape, and have importance in the development of new varieties of orchids
A full length cDNA (DhMYB1) was amplified from D. hybrida flower RNA using the partial R2R3 MYB sequence that is monophyletic with AmMIXTA and the translated full length sequence used for phylogenetic analysis, that grouped it together with DwMYB1 and DcMYBML1, whilst its sister group contained AmMIXTA and AmMYBML1 (Fig. 2)
The development of Dendrobium hybrida flower buds was characterised into seven stages with meiosis occurring between stages 3 to 5 and pollen formation estimated to occur at stage 6
Summary
The R2R3-MYB genes regulate pigmentation and morphogenesis of flowers, including flower and cell shape, and have importance in the development of new varieties of orchids. Orchids, belonging to the family Orchidaceae, one of the largest and most evolved families among flowering plants [1] have a wide variety of attractive shapes and colours, long flowering life and availability throughout the year. This contributes to the economic importance of the Factors that determine flower colour include secondary metabolites, pH value, metal ions, flavonoid co-pigments, Lau et al BMC Plant Biology (2015) 15:194 environmental temperature and morphology of the epidermal cells [3, 4]. It has been suggested that a conical cell shape could enhance light absorption by the pigments by increasing the amount of incident light that enters the epidermal cells [10,11,12]
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