Tissue-specific profiles of phenolic metabolites in rice deprived of OsCOP1, OsDET1, and OsCGT

Colored rice is recognized for its health-promoting properties, particularly its strong antioxidant activity. However, comparative analyses of phenolic metabolites across seed tissues and flavonoids beyond anthocyanidins remain limited. A comprehensive understanding of tissue-specific phenolic distribution and the regulatory mechanisms governing flavonoid diversification is essential for targeted metabolic engineering of nutritionally enhanced rice. This study analyzed phenolic metabolite profiles in the yellowish-pericarp embryo lethal ( yel ) mutant rice, which accumulates excessive C- glycosylated flavones as a result of loss-of-function mutations in CONSTITUTIVELY PHOTOMORPHOGENIC 1 ( COP1 ) or DE-ETIOLATED 1 ( DET1 ), and in a double mutant deficient in C- glycosyltransferase (CGT) function. Using comparative metabolomic profiling across embryo and endosperm tissues of four genetic backgrounds, we quantitatively characterized alterations in flavone composition associated with specific regulatory mutations. In all mutants, embryos accumulated higher levels of phenolics than the endosperm. In the yel mutant, C- glycosyl flavones, such as isoorientin, markedly increased, whereas they decreased in the double mutant. These compositional and quantitative changes were consistent across the four cultivars. Interestingly, anthocyanins were not detected, despite yellow or purple pericarp phenotypes in both mutant types. Our findings demonstrate that OsCOP1 and OsDET1 act as key upstream regulators of flavone biosynthesis, whereas OsCGT is critical for C- glycosylation-mediated metabolic flux toward stable flavone derivatives. This work elucidates the effects of OsCOP1 , OsDET1 , and OsCGT on flavonoid biosynthesis via metabolomics, providing key data for functionally enhanced rice breeding. Collectively, these results provide insights into the potential link between light signaling components and phenolic metabolism in rice grains. Our findings suggest practical strategies for utilizing these genetic components in the development of cultivars with enhanced flavone content.