Abstract
Osmanthus fragrans is widely grown for the purpose of urban greening and the pleasant aroma emitted from its flowers. The floral scent is determined by several monoterpenoid volatiles, such as linalool and its oxides, which are a few of the most common volatiles and the main components of the essential oils in most sweet osmanthus cultivars. In addition, the relative contents of cis- and trans-linalool oxide (furan) may affect the aromas and quality of the essential oils. MYB proteins represent the largest family of transcription factors in plants and participate in regulating secondary metabolites. Several cis-elements, especially AC-rich regions, are known to be bound by 2R-MYBs and could be found in the promoter of the enzyme genes in the terpenoid metabolic pathway. However, there has to date been no investigation into the 2R-MYB family genes involved in regulating terpenoid biosynthesis in O. fragrans. Here, 243 non-redundant 2R-MYB proteins were grouped into 33 clusters based on the phylogeny and exon-intron distribution. These genes were unevenly distributed on 23 chromosomes. Ka/Ks analysis showed that the major mode of 2R-MYB gene evolution was purifying selection. Expression analysis indicated that 2R-MYB genes in O. fragrans exhibited varied expression patterns. A total of 35 OfMYBs representing the highest per kilobase per million mapped reads in the flower were selected for quantitative real-time PCR analysis. The correlation analysis between the expression level and the contents of fragrant compounds at different flowering stages suggested that OfMYB19/20 exhibited remarkably positive correlation with the accumulation of cis-linalool oxides. OfMYB51/65/88/121/137/144 showed significantly negative correlations with one or more linalool oxides. Characterization of these proteins revealed that OfMYB19 and OfMYB137 were localized in the nuclei, but did not show transcriptional activation in the yeast system, which suggested that they may be bound to other transcription factors to exert regulatory functions. These findings provide useful information for further functional investigation of the 2R-MYBs and offer a foundation for clarifying the 2R-MYB transcription factors involved in the molecular mechanism of the regulation of monoterpenoid biosynthesis in Osmanthus fragrans.
Highlights
Transcription factors (TFs) are important proteins that bind special cis-acting elements to affect the expression of target genes by modulating the transcription rate [1]
Fresh flowers in the different flowering stages were used to detect the scent compounds with the method of head space solid phase microextraction(HS-SPME) and gas chromatography/mass spectrometer (GC/MS); the detailed information was stated and the results presented in our previous work [15,30]
Most of the subgroups included the Arabidopsis and sweet osmanthus MYB proteins, indicating that members of the same subgroup shared a common evolutionary origin and that most MYB genes were functionally conserved during evolution
Summary
Transcription factors (TFs) are important proteins that bind special cis-acting elements to affect the expression of target genes by modulating the transcription rate [1]. The COLORED1 (C1) locus encoding an MYB domain protein was first identified in plants. This locus is related to anthocyanin synthesis in maize (Zea mays) kernels [11]. The functions of a considerable number of 2R-MYB proteins have been investigated in different plant species. These proteins are thought to be involved in defense and responses to various biotic and abiotic stresses, cell development, control of the cell cycle, and regulating primary and secondary metabolism [3,5]
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