Abstract
Geranyl diphosphate synthase (GPPS) is a plastid localized enzyme that catalyzes the biosynthesis of Geranyl diphosphate (GPP), which is a universal precursor of monoterpenes. Wintersweet (Chimonanthus praecox L.), a famous deciduous flowering shrub with a strong floral scent character, could have GPPS-like homologs that are involved in monoterpenes biosynthesis, but it remains unclear. In the present study, five full-length GPPS and geranylgeranyl diphosphate synthases (GGPPS) genes were identified in the wintersweet transcriptome database. The isolated cDNAs showed high protein sequence similarity with the other plants GPPS and GGPPS. The phylogenetic analysis further classified these cDNAs into four distinct clades, representing heterodimeric GPPS small subunits (SSU1 and SSU2), homodimeric GPPS, and GGPPS. Analysis of temporal expression revealed that all genes have the highest transcript level at the full-open flower stage. From tissue-specific expression analysis, CpGPPS.SSU1 and CpGGPPS1 were predominantly expressed in petal and flower, whereas CpGPPS.SSU2, GPPS, and GGPPS2 showed a constitutive expression. Additionally, the subcellular localization assay identified the chloroplast localization of SSUs and GGPPSs proteins, and the yeast two-hybrid assay showed that both CpGPPS.SSU1 and CpGPPS.SSU2 can interact with the GGPPS proteins. Taken together, these preliminary results suggest that the heterodimeric GPPS can regulate floral scent biosynthesis in wintersweet flower.
Highlights
The floral scent is one of the main features that define the aesthetic value of cut flowers and ornamental plants [1]
From the floral cDNA library of the C. praecox plant, eight cDNAs were found to be annotated as Geranyl diphosphate synthase (GPPS)/geranylgeranyl diphosphate synthases (GGPPS), of which five cDNAs had full-length open reading frames (ORF)
(57.89%), followed by a sudden decline at senescence (9.44%). These results suggest that the spatiotemporal expression of CpGPPS.SSU1 and CpGGPPS1 is strictly confined to the scent-emitting tissues with a good association to monoterpene contents
Summary
The floral scent is one of the main features that define the aesthetic value of cut flowers and ornamental plants [1]. It is made up of the specialized metabolites of plants, which enable them to interact with their environment by attracting pollinators and repelling pests, such as herbivores, pathogens, and parasites [2]. The floral scent is the composite of different volatile organic compounds (VOCs), which mainly include terpenoids, phenylpropanoids, benzenoid compounds, and fatty acid derivatives [3]. The content and composition of VOCs vary among species and contribute to their distinct fragrance [4]. Terpenoids account for a range of secondary metabolites with numerous volatile constituents, which are derived from two interconvertible five-carbon (C5) precursors (isopentenyl diphosphate (IPP) and its allylic isomer, dimethylallyl diphosphate (DMAPP)) [5].
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