Transgenic rice lines expressing maize C1 and R-S regulatory genes produce various flavonoids in the endosperm.
Flavonoids, compounds that possess diverse health-promoting benefits, are lacking in the endosperm of rice. Therefore, to develop transgenic lines that produce flavonoids, we transformed a white rice cultivar, Oryza sativa japonica cv. Hwa-Young, with maize C1 and R-S regulatory genes. Expression of these transgenes was restricted to the endosperm using the promoter of a rice prolamin gene. The pericarp of the C1/R-S homozygous lines became dark brown in accordance with their maternal genotype, whereas the endosperm turned chalky, similar to the opaque kernel phenotype. Analysis via high-performance liquid chromatography (HPLC) revealed that numerous kinds of flavonoids were produced in these transgenic kernels. To identify individual flavonoids, the number of HPLC peaks was reduced through moderate acid hydrolysis, followed by ethyl acetate partitioning. Amongst the major flavonoids, dihydroquercetin (taxifolin), dihydroisorhamnetin (3'-O-methyl taxifolin) and 3'-O-methyl quercetin were identified through liquid chromatography/mass spectrometry/mass spectrometry and nuclear magnetic resonance analyses. Fluorescence labelling with diphenylboric acid showed that the flavonoids were highly concentrated in the cells of four to five outer endosperm layers. More importantly, a high fluorescence signal was present in the cytosol of the inner endosperm layers. However, the overall signal in the inner layers was significantly lower because starch granules and protein bodies occupied most of the cytosolic space. Our estimate of the total flavonoid content in the transgenic kernels suggests that C1/R-S rice has the potential to be developed further as a novel variety that can produce various flavonoids in its endosperm.
Shin
Young-Mi
YM
Kumho Life & Environmental Science Laboratory, 1 Oryong-Dong, Puk-Gu, Kwangju 500-712, South Korea.
Park
Hee-Jin
HJ
Yim
Sun-Duck
SD
Baek
Nam-In
NI
Lee
Choong-Hwan
CH
An
Gynheung
G
Woo
Young-Min
YM
D002851:Chromatography, High Pressure Liquid; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005419:Flavonoids / Q000096:biosynthesis* / Q000737:chemistry; D012275:Oryza / Q000033:anatomy & histology / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000033:anatomy & histology / Q000378:metabolism*; D012639:Seeds / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014170:Transformation, Genetic; D019076:Transgenes; D003313:Zea mays / Q000235:genetics*
C067401:C1 protein, Zea mays; D004268:DNA-Binding Proteins; D005419:Flavonoids; D010940:Plant Proteins; D014157:Transcription Factors