Abstract
Flavonoids are representative secondary metabolites with different metabolic functions in plants. Previous study found that ectopic expression of EsMYB90 from Eutrema salsugineum could strongly increase anthocyanin content in transgenic tobacco via regulating the expression of anthocyanin biosynthesis genes. In the present research, metabolome analysis showed that there existed 130 significantly differential metabolites, of which 23 metabolites enhanced more than 1000 times in EsMYB90 transgenic tobacco leaves relative to the control, and the top 10 of the increased metabolites included caffeic acid, cyanidin O-syringic acid, myricetin and naringin. A total of 50 markedly differential flavonoids including flavones (14), flavonols (13), flavone C-glycosides (9), flavanones (7), catechin derivatives (5), anthocyanins (1) and isoflavone (1) were identified, of which 46 metabolites were at a significantly enhanced level. Integrated analysis of metabolome and transcriptome revealed that ectopic expression of EsMYB90 in transgenic tobacco leaves is highly associated with the prominent up-regulation of 16 flavonoid metabolites and the corresponding 42 flavonoid biosynthesis structure genes in phenylpropanoid/flavonoid pathways. Dual luciferase assay documented that EsMYB90 strongly activated the transcription of NtANS and NtDFR genes via improving their promoter activity in transiently expressed tobacco leaves, suggesting that EsMYB90 functions as a key regulator on anthocyanin and flavonoid biosynthesis. Taken together, the crucial regulatory role of EsMYB90 on enhancing many flavonoid metabolite levels is clearly demonstrated via modulating flavonoid biosynthesis gene expression in the leaves of transgenic tobacco, which extends our understanding of the regulating mechanism of MYB transcription factor in the phenylpropanoid/flavonoid pathways and provides a new clue and tool for further investigation and genetic engineering of flavonoid metabolism in plants.
Highlights
Introduction iationsFlavonoids, as the most ancient and vital secondary metabolites in plants, are determinants of crop quality and commercial value because they influence many characteristics of plant tissue including color, nutritive value, aroma and antioxidant properties [1]
We demonstrated that ectopic expression of Eutrema EsMYB90 (p35S:EsMYB90) in tobacco led to purplish red at varying degrees in leaves, stem, flowers and fruit pods and was accompanied with a strongly elevated anthocyanin level [37]
We found that the contents of total flavonoid and anthocyanin in young leaves (YL), mature leaves (ML), stems and roots in EsMYB90 transgenic tobacco line 2line (L2) and L4 lines ments and flavonoid compounds, the contents of anthocyanin, chlorophyll, proanthocya4 of 19 nin (PA) and total flavonoid were checked in EsMYB90 transgenic tobacco and wild type plants
Summary
Flavonoids, as the most ancient and vital secondary metabolites in plants, are determinants of crop quality and commercial value because they influence many characteristics of plant tissue including color, nutritive value, aroma and antioxidant properties [1]. Accumulation of flavonoids is favorable for plants because they provide plants with color for most flowers, fruits and seeds to attract pollinators, and light-shielding, metal-binding and antioxidant capacities and functions in osmotic regulation [3,4,5]. A common factor with abiotic stress is the accumulation of ROS [6]. Flavonoids, acting as scavengers of ROS, can be induced by many environmental stimuli to protect plants against diverse abiotic and biotic stresses [6,7]. Flavonoids are classified into several subgroups including anthocyanin, proanthocyanidin (PA or condensed tannin), Licensee MDPI, Basel, Switzerland
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