Metabolic diversity analysis and genome wide assessment of oxalate accumulation in the leaves of rice (Oryza sativa) cultivars

Soluble oxalate accumulates in rice leaves, and it causes mineral deficiency and urinary syndrome in livestock that consume the leaves. In our previous study, we found that the oxalate content was higher in the leaves of Koshihikari (japonica type cultivar) than in those of Takanari (indica type cultivar). This difference was seen even when the two cultivars were grown under a high CO₂ concentration, which inhibits oxalate synthesis via photorespiration, suggesting that the difference resulted from genetic factors rather than environmental factors. To clarify whether genetic factors affect the oxalate content of rice leaves, we measured the contents of oxalate and oxalate-related organic acids in the leaves of various rice cultivars the Rice Core Collection (WRC) and Japan Rice Core Collection (JRC) by capillary electrophoresis-mass spectrometry. Results showed that japonica type cultivars tended to accumulate more oxalate than aus or indica type cultivars. Correlation analysis revealed a positive correlation between oxalate accumulation and the citrate content, suggesting that the isocitrate pathway is involved in oxalate accumulation. On the other hand, a genome-wide association study for the oxalate content of the WRC and JRC cultivars did not reveal significant loci directly related to oxalate accumulation. This indicates that the combination of various loci may affect the oxalate contents of rice leaves.