Metabolite Variation in Genetically Distinct Rice Cultivars: Implications for Human Nutrition and Health.

The identification of plant phytochemicals as important bioactive food components is an emerging field. However, the relative amounts and types of metabolites in our foods are largely unknown. Metabolomics was performed to to investigate small molecules present in cooked brown rice (Orzya sativa) and isolated rice bran. Varieties of rice were chosen based on significant genetic diversity and distinct grain characteristics.  A standard operating procedure was developed in our laboratory for analysis of the rice metabolome and methanol-soluble compounds were extracted and detected by liquid chromatography-mass spectrometry. The relative abundance and uniqueness of the metabolites were assessed by principal components analysis. A total of 3662 features were detected in the reference rice variety Nipponbare (japonica family). 446 candidate metabolites were determined to have a minimum fold-change peak intensity difference of 2 or greater between Nipponbare and IR64, an indica rice variety genetically distinct from Nipponbare. These candidate molecules were either specific to one rice variety or had a larger presence in one variety over another. A total of 567 candidate metabolites were unique or exhibited  a greater presence between IR64 and Moroberekan (African japonica variety) that accounts for approximately 7% of the total rice metabolites detected. The capability to generate unique metabolomic profiles for highly consumed rice varieties has potential for future investigations of bioactive food components in rice and a better understanding of how rice can be improved for disease prevention. We propose that an integration of the metabolome with the  rice seed transcriptome will be a valuable systems biology approach for crop improvement through the identification of genes that influence the metabolic phenotype.