Characterization of a Hybrid Population from a Cross between a Black Waxy Rice Cultivar and Transgenic Rice with High Levels of Flavonoids in the Endosperm

Flavonoids in the diet are known to exhibit health-beneficial effect on humans. In order to enhance the nutritional value of rice with health-beneficial flavonoids, we developed rice lines using transgenic rice with high levels of flavonoids. The transgenic rice was produced through the expression of maize C1 and R-S regulatory genes in the endosperm of a white rice cultivar, Oryza sativa spp japonica cv Hwayeong, designated as Green Tea Rice (GTR). The total flavonoid contents in the GTR seeds were 14 and 6 times higher than those of the non-transgenic white rice Hwayeong and the black rice cultivar Josaengheugchal (JSHC), respectively. The GTR lines, however, exhibited a reduction in grain filling up to 65% depending on growing conditions. To improve grain filling and widen the spectrum of flavonoid contents in the grain, transgenic lines were crossed to a black colored waxy rice cultivar JSHC. Due to multiple genes associated with anthocyanin accumulation in the pericarp of JSHC, F(2) Progenies segregated into diverse seed phenotypes including pericarp color, seed weight, and seed sizes. The sublines carrying maize C1 and R-S transgenes exhibited pericarp pigmentation similar to that of the GTR parent Grain filling of such lines was nearly similar to the donor cultivar Hwayeong by 89% and 50% better than the GTR parent Although the total flavonoid content of the sublines was 1.3 fold higher than that of the JSHC parent, it was only 33% that of GTR's. Correlation value (r = -0.82, n=3) between flavonoid content and grain weight suggest that flavonoid content and grain filling could be linked in the hybrid sublines and high variation exists in the progenies. Further selection of hybrid sublines for optimal flavonoid contents with improved grain filling is in progress.