Dosage effect of anthocyanin biosynthesis in purple-grained wheat ( Triticum aestivum L.)

Purple color of the wheat grain is due to the accumulation of anthocyanins in the pericarp and is genetically controlled by two complementary regulatory genes, namely TaPpm1 and TaPpb1 . To study their complementary mechanism, six crosses were made with 3 pairs of nonpurple-grained DH lines and an EMS-induced mutant, which were derived from the white-grained parent Liangxing99 (LX99) and/or purple-grained Nongda3753 (ND3753), respectively. As expected, the purple character was successfully recovered in all the F 1 progeny, although their seed color was visually lighter than that of ND3753 to various extents. The cross between DH41 ( TaPpm1a / TaPpb1b ) and DH33 ( TaPpm1d / TaPpb1a ), which showed the deepest seed color in all of the progeny, was used to further investigate related genes expression and anthocyanin accumulation. Measurement of anthocyanin content across five grain developing stages showed that the accumulation of anthocyanin in seeds of DH41/DH33 was lower and later than that of ND3753. Detection of expression patterns of two regulatory genes revealed that TaPpb1 expressed quite consistently in double-locus heterozygous, double-locus dominant homozygous, and single-locus dominant homozygous, whereas the expression of TaPpm1 showed a significant difference in different states. It was highly expressed in the double-locus homozygous genotype in the early grain developing stage and increased expression in double-locus heterozygous in the late stage but remained low level in single-locus homozygous in all stages. Furthermore, expression patterns of seven structural genes involved in anthocyanin biosynthesis were investigated, among which F3'H , DFR , and ANS were in accordance with that of TaPpm1 and the anthocyanin accumulation. Thus, the dosage effect of wheat purple grain color was a result of delayed expression of one of the two regulatory genes, namely TaPpm1 in the heterozygous genotype, and consequently the reduced expression of middle and later structural genes in anthocyanin biosynthesis pathway in grain development.