Abstract
Comprehensive profiling of primary and secondary metabolites was performed to understand metabolic differences associated with color formation in pigmented rice (Oryza sativa L.). Overall, 110 metabolites from non-pigmented, black, and red rice cultivars were identified. Black and red rice contained high levels of flavonoids associated with plant color. Black rice also contained high levels of terpenoids (carotenoids, tocopherols, phytosterols, and monoterpenes). The non-pigmented rice contained relatively low levels of secondary metabolites. Multivariate and pathway analyses were performed to data-mine the metabolite profiles. Hierarchical clustering analysis of correlation coefficients revealed metabolite clusters based on nitrogen and carbon sources. These clusters suggested a negative correlation between nitrogen and carbon. Pathway analysis revealed that black rice was rich in carbon-based secondary metabolites, with relatively low levels of primary metabolites compared with other rice cultivars. These data highlight the complex interactions between nitrogen and carbon metabolism of primary and secondary metabolites in rice. For the first time, the relationships and metabolic differences in terpenoid content (monoterpenes, triterpenes, and tetraterpenes) of non-pigmented and pigmented rice cultivars were analyzed. These findings should greatly contribute to the understanding of pigmented rice metabolome and inform breeding programs for new rice cultivars.
Highlights
Multivariate statistical analysis is an important tool used for obtaining an overview of patterns in complex experimental data
Principal component analysis (PCA) is a preliminary step in a multivariate analysis performed to discern novel information hidden in the big data
PCA did not reveal a clear separation of the rice seeds by color (Figure S1)
Summary
Rice (Oryza sativa L.) is a staple diet for over half of the world’s population and is the second largest cultivated cereal crop worldwide [1,2]. Pigmented rice comes in various colors, such as black, red, and green. The major coloring agents in black rice (BR) are anthocyanins, such as cyanidin-3-O-glucoside and peonidin-3-O-glucoside, whereas those in red rice (RR) are proanthocyanidins and flavan-3-ols oligomers, with catechin as the main synthesis unit [3,4]. Consumption of pigmented rice is associated with several health benefits, for example, antioxidant, anti-cancer, anti-tumor, anti-diabetic, and cardiovascularprotective activities [5]
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