Abstract
Anthocyanins (a subclass of flavonoids) and flavonoids are crucial determinants of flower color and substances of pharmacological efficacy, respectively, in chrysanthemum. However, metabolic and transcriptomic profiling regarding flavonoid accumulation has not been performed simultaneously, thus the understanding of mechanisms gained has been limited. We performed HPLC-DAD-ESI-MS (high-performance liquid chromatography coupled with photodiode array detection and electrospray ionization mass spectrometry) and transcriptome analyses using “ARTI-Dark Chocolate” (AD), which is a chrysanthemum mutant cultivar producing dark-purple ray florets, and the parental cultivar “Noble Wine” for metabolic characterization and elucidation of the genetic mechanism determining flavonoid content. Among 26 phenolic compounds identified, three cyanidins and eight other flavonoids were detected only in AD. The total amounts of diverse flavonoids were 8.0 to 10.3 times higher in AD. Transcriptome analysis showed that genes in the flavonoid biosynthetic pathway were not up-regulated in AD at the early flower stage, implying that the transcriptional regulation of the pathway did not cause flavonoid accumulation. However, genes encoding post-translational regulation-related proteins, especially F-box genes in the mutated gene, were enriched among down-regulated genes in AD. From the combination of metabolic and transcriptomic data, we suggest that the suppression of post-translational regulation is a possible mechanism for flavonoid accumulation in AD. These results will contribute to research on the regulation and manipulation of flavonoid biosynthesis in chrysanthemum.
Highlights
The flavonoids are a class of phenylpropanoids with a C6-C3-C6 carbon skeleton comprising more than 10,000 structures [1]
“ARTI-Dark Chocolate” is a mutant cultivar producing dark purple ray florets developed by γirradiation
865an original cultivar, “Noble Wine”, that produces very light pink ray florets with purple-colored strips (Figure 1A; hereafter, NW and ARTI-Dark Chocolate” (AD) will be used as abbreviations for Noble Wine and ARTI-Dark Chocolate, respectively)
Summary
The flavonoids are a class of phenylpropanoids with a C6-C3-C6 carbon skeleton comprising more than 10,000 structures [1]. We have developed a series of chrysanthemum mutant cultivars by γ-irradiation on “Noble Wine”, which is a spray-type Korean commercial cultivar with bright stripes on multiple flowers One such mutant cultivar, “ARTI-Yellow Star”, has yellow ray florets and was revealed to highly accumulate carotenoids [28]. The deletion of CmCCD4a genes that have been reported to degrade carotenoids was detected [28] Another mutant cultivar, “ARTI-Dark Chocolate”, which produces dark purple ray florets, was revealed to accumulate a large amount of flavonoids and have strong antioxidant capacity [29]. We performed high-performance liquid chromatography coupled with photodiode array detection and electrospray ionization mass spectrometry (HPLC-DAD-ESI-MS) and transcriptome analysis using an artificially mutated chrysanthemum cultivar that produces dark purple ray florets to characterize flavonoid content in the ray floret corolla and to elucidate the mechanism of flavonoid accumulation
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