Abstract
Prunus mume, a traditional Chinese flower, is the only species of Prunus known to produce a strong floral fragrance, of which eugenol is one of the principal components. To explore the molecular mechanism of eugenol biosynthesis in P. mume, patterns of dynamic, spatial and temporal variation in eugenol were analysed using GC-MS. Coniferyl alcohol acetyltransferase (CFAT), a member of the BAHD acyltransferase family, catalyses the substrate of coniferyl alcohol to coniferyl acetate, which is an important substrate for synthesizing eugenol. In a genome-wide analysis, we found 90 PmBAHD genes that were phylogenetically clustered into five major groups with motif compositions relatively conserved in each cluster. The phylogenetic tree showed that the PmBAHD67-70 proteins were close to the functional CFATs identified in other species, indicating that these four proteins might function as CFATs. In this work, 2 PmCFAT genes, named PmCFAT1 and PmCFAT2, were cloned from P. mume ‘Sanlunyudie’, which has a strong fragrance. Multiple sequences indicated that PmCFAT1 contained two conserved domains, HxxxD and DFGWG, whereas DFGWG in PmCFAT2 was changed to DFGFG. The expression levels of PmCFAT1 and PmCFAT2 were examined in different flower organs and during the flowering stages of P. mume ‘Sanlunyudie’. The results showed that PmCFAT1 was highly expressed in petals and stamens, and this expression increased from the budding stage to the full bloom stage and decreased in the withering stage, consistent with the patterns of eugenol synthesis and emission. However, the peak of gene expression appeared earlier than those of eugenol synthesis and emission. In addition, the expression level of PmCFAT2 was higher in pistils and sepals than in other organs and decreased from the budding stage to the blooming stage and then increased in the withering stage, which was not consistent with eugenol synthesis. Subcellular localization analysis indicated that PmCFAT1 and PmCFAT2 were located in the cytoplasm and nucleus, while enzyme activity assays showed that PmCFAT1 is involved in eugenol biosynthesis in vitro. Overall, the results suggested that PmCFAT1, but not PmCFAT2, contributed to eugenol synthesis in P. mume.
Highlights
Floral scents play important and significant roles as attractants for pollinators and defence compounds against animals and microorganisms [1, 2]
The results suggested that PmCFAT1, but not PmCFAT2, contributed to eugenol synthesis in P. mume
The extracted eugenol amounts in the petals and stamens were higher than those in the other two organs, the eugenol content was higher in petals than in stamens
Summary
Floral scents play important and significant roles as attractants for pollinators and defence compounds against animals and microorganisms [1, 2]. Floral scents can raise the aesthetic value of ornamental plants and benefit human health [3]. Many plants have lost their fragrance because breeding objectives were focused on flower type, colour, long vase life and so on [4]. Is a famous traditional Chinese ornamental tree with a long history of cultivation and emits a recognizable pleasant floral scent unlike other Prunus species [5]. Studies have shown that eugenol is the most important constituent of the characteristic floral scent of P. mume [6]. There is little eugenol in these plants, its odour perception threshold is low, making it possible for this scent to be the characteristic scent [8]
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