Abstract
Mizuna (Brassica rapa L. var. japonica), a member of the family Brassicaceae, is rich in various health-beneficial phytochemicals, such as glucosinolates, phenolics, and anthocyanins. However, few studies have been conducted on genes associated with metabolic traits in mizuna. Thus, this study provides a better insight into the metabolic differences between green and red mizuna via the integration of transcriptome and metabolome analyses. A mizuna RNAseq analysis dataset showed 257 differentially expressed unigenes (DEGs) with a false discovery rate (FDR) of <0.05. These DEGs included the biosynthesis genes of secondary metabolites, such as anthocyanins, glucosinolates, and phenolics. Particularly, the expression of aliphatic glucosinolate biosynthetic genes was higher in the green cultivar. In contrast, the expression of most genes related to indolic glucosinolates, phenylpropanoids, and flavonoids was higher in the red cultivar. Furthermore, the metabolic analysis showed that 14 glucosinolates, 12 anthocyanins, five phenolics, and two organic acids were detected in both cultivars. The anthocyanin levels were higher in red than in green mizuna, while the glucosinolate levels were higher in green than in red mizuna. Consistent with the results of phytochemical analyses, the transcriptome data revealed that the expression levels of the phenylpropanoid and flavonoid biosynthesis genes were significantly higher in red mizuna, while those of the glucosinolate biosynthetic genes were significantly upregulated in green mizuna. A total of 43 metabolites, such as amino acids, carbohydrates, tricarboxylic acid (TCA) cycle intermediates, organic acids, and amines, was identified and quantified in both cultivars using gas chromatography coupled with time-of-flight mass spectrometry (GC-TOFMS). Among the identified metabolites, sucrose was positively correlated with anthocyanins, as previously reported.
Highlights
Plant species of the family Brassicaceae, previously called Cruciferae, have long been considered health-boosting vegetables and are commonly cultivated worldwide because they provide high amounts of dietary minerals, amino acids, carbohydrates, fatty acids, dietary fibers, vitamins, and bioactive molecules, including glucosinolates, phenylpropanoids, anthocyanins, and carotenoids
The correlations between sucrose and 12 anthocyanins identified revealed a positive effect of sucrose on anthocyanin production, as supported by previous studies reporting the effect of sucrose on anthocyanin biosynthesis
Anthocyanins identified revealed a positive effect of sucrose on anthocyanin production, as supported the high-throughput transcriptome data, the primary metabolite biosynthesis genes, including three by previous reporting the effectand of sucrose on related anthocyanin biosynthesis
Summary
Plant species of the family Brassicaceae, previously called Cruciferae, have long been considered health-boosting vegetables and are commonly cultivated worldwide because they provide high amounts of dietary minerals, amino acids, carbohydrates, fatty acids, dietary fibers, vitamins (tocopherol, ascorbate, and folate), and bioactive molecules, including glucosinolates, phenylpropanoids, anthocyanins, and carotenoids. We analyzed the transcriptome and metabolome of these two cultivars using the Illumina Solexa platform, GC-TOFMS, liquid chromatography electrospray ionization tandem mass spectrometric (LC-ESI-MS), and high-performance liquid chromatography (HPLC) and comprehensively described the relationship between all identified metabolites To our knowledge, this is the first study to provide information on metabolic differences between green and red mizuna through transcriptome and metabolome analyses.
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