Accumulation of Polymethoxyflavones and O-methyltransferase Gene Expression in Various Citrus Cultivars

• Published in: Horticulture journal 2020, Vol.89(3), pp.225-236
• Main Authors: Zohra, Fatema Tuz, Takematsu, Shotaro, Itami, Yuri, Kotoda, Nobuhiro
• Format: Article
• Language: English
• Subjects: Accumulation; Biosynthesis; Cultivars; flavedo; flavone; Flavones; Gene expression; Geographical distribution; HPLC; Leaves; Methyltransferase; nobiletin; Plant breeding; Seedlings; Tangeretin
• ISSN: 2189-0102; 2189-0110
• DOI: 10.2503/hortj.UTD-146

Polymethoxyflavones (PMFs) are naturally occurring O-methylated flavones predominantly accumulated in different citrus tissues that show numerous human-health promoting activities. O-methyltransferase (OMT) family members are involved in the biosynthesis of PMFs in plant species including citrus. Although the distribution of PMFs has been determined in citrus cultivars, the relation between the accumulation of PMFs and the related OMT gene expression in leaves and flavedos (exocarps) of citrus cultivars remains to be clarified. In this study, we investigated the accumulation of nobiletin and tangeretin in the leaves and flavedos of various citrus cultivars widely grown in Japan. As expected, the accumulation of nobiletin and tangeretin varied among the citrus cultivars and the two tissues, and nobiletin and tangeretin accumulated at higher levels in flavedos than in leaves. In particular, we clearly demonstrated that the nobiletin content showed a significant and positive correlation (r = 0.824, P = 0.00182) between leaves and flavedos. Based on these results, the concentration of PMFs in leaves could be utilized as an early selection marker for seedlings in the juvenile phase that are expected to accumulate a higher amount of PMFs in fruit, resulting in a shortening of the breeding period. We also identified two novel candidate genes, CreOMT1 and CreOMT4, putatively involved in PMF biosynthesis in citrus. Notably, the expression of CreOMT1 showed a significant correlation (r = 0.700, P = 0.0243) with the nobiletin content in the flavedos of 10 citrus cultivars. Our results provide valuable information for developing new citrus cultivars that could accumulate higher PMFs and insight into elucidating the PMF biosynthetic pathway in citrus in the future.