|ZAREI, IMAN - Colorado State University|
|LUNA, EMILY - Colorado State University|
|LEACH, JAN - Colorado State University|
|VILCHEZ, SAMUEL - Universidad De Nicaragua|
|OUSMANE, KOITA - University Of Bamako|
|RYAN, ELIZABETH - Colorado State University|
Submitted to: Metabolites
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2018
Publication Date: 10/9/2018
Citation: Zarei, I., Luna, E., Leach, J.E., McClung, A.M., Vilchez, S., Ousmane, K., Ryan, E.P. 2018. Comparative rice bran metabolomics across diverse cultivars and functional rice gene-bran metabolite relationships. Metabolites. https://doi.org/10.3390/metabo8040063.
Interpretive Summary: During the rice milling process, the bran is removed to produce whole milled rice. Although some bran is used to produce rice bran oil, most bran is sold as inexpensive animal feed. Recent research has demonstrated that rice bran contains a number of nutritional compounds, namely bioactive metabolites, that are of benefit to human and animal health. Dietary consumption of rice bran has been shown to increase key nutrients and fiber intakes and provide health promoting properties in the prevention and control of major chronic diseases, such as diabetes, chronic inflammation, cardiovascular disease, as well as cancers of colon, liver, prostate, and breast. There is limited information on how much variation exists among global rice cultivars for these bioactive compounds. The objective of this study was to investigate variation in the rice bran metabolome of 17 diverse cultivars and to identify genes and physiological pathways relevant to the nutritional and medicinal quality of rice bran. The total number of metabolites identified ranged from 378 for the variety Njavara produced in India to 430 for the variety Gambiaka grown in Mali. Of the US developed varieties, Calrose medium grain rice, produced in California, had the highest total number of metabolites (421). Among the total number of compounds observed, 71 were found to differ in relative abundance among the 17 rice cultivars. Metabolites that are associated with lipids accounted for about 40% of the total metabolites. Rice bran is known to be a good source of the lipid soluble vitamin E which is an important antioxidant and free-radical scavenger that contributes to the bioactivity of rice bran. These results indicate that there is genetic variability for rice bran metabolites, many of which are associated with health beneficial properties, which affords the possibility of developing new rice cultivars with enhanced nutritional value.
Technical Abstract: Rice bran provides essential nutrients and phytochemicals for animal and human health. Rice is grown in over a hundred countries and produces more than 60 million metric tons of bran annually. Rice bran metabolites were hypothesized to exhibit biochemical variation and reveal key rice gene-metabolite relationships of utility for novel rice bran nutrition and health quality traits. Rice bran was isolated from 17 diverse rice cultivars sourced from seven countries. Fourteen had brown colored bran while three had red or purple bran. The bran was evaluated for total metabolite composition using non-targeted metabolomics via ultrahigh performance liquid chromatography-tandem mass spectrometry. Metabolite profiling yielded a range of 378-430 metabolites across the 17 cultivars. The largest number of total metabolites was identified from the Gambiaka cultivar and the lowest from the Njavara. Cultivar variation in the metabolome was described by principal component analysis (PCA) as 20.3% for PC1 and 16% for PC2. Individual metabolite comparisons by Z-score showed 71 rice bran compounds, including 21 amino acids, seven carbohydrates, two metabolites from cofactors and vitamins, 33 lipids, six nucleotides, and two secondary metabolites. These 71 rice bran metabolites with significant differences in relative abundance across the 17 cultivars were clustered into six chemical classes and were associated with 15 metabolic pathways. N-methylproline, stachydrine, and trans-4-hydroxyproline are classified as glutamate family (alphaketoglutarate derived) amino acids, and were highest in abundance for Gambiaka from Mali. Gamma-tocopherol/beta-tocopherol and gamma-tocotrienol from the vitamin E metabolic pathway under the cofactors and vitamins chemical class were lowest in relative abundance in Sawa Mahsuli from Nepal when compared to other brans. The biosynthetic genes for 71 bran metabolites that varied between rice cultivars were identified using the OryzaCyc 4.0, Plant Metabolic Network database, and 24 genes and seven chromosomes were implicated in vitamin E component production, an important antioxidant and free-radical scavenger that contributes to the bioactivity of rice bran. Rice genes responsible for bran metabolites have animal and human health importance and these findings suggest a practical starting point for rice breeding programs to consider crop improvement strategies for bran composition