Identification of Two Anthocyanidin Reductase Genes and Three Red-Brown Soybean Accessions with Reduced <i>Anthocyanidin Reductase 1</i> mRNA, Activity, and Seed Coat Proanthocyanidin Amounts

Abstract

Anthocyanidin reductase (ANR; EC 1.3.1.77) catalyzes a key step in the biosynthesis of proanthocyanidins (PAs; also known as condensed tannins), flavonoid metabolites responsible for the brown pigmentation of seeds. Here, two ANR genes (<i>ANR1</i> and <i>ANR2</i>) from the seed coat of brown soybean (Glycine max (L.) Merr.) have been isolated and their enzymatic function confirmed for the reduction of cyanidin to (−)-epicatechin in vitro. Biochemical and genetic comparisons of soybean lines differing in seed coat color revealed three red-brown lines to exhibit major reductions in the amounts of soluble PAs in the seed coat compared to brown soybean lines. Two spontaneous mutants with red-brown grain color had reduced <i>ANR1</i> gene expression in the seed coat, and an EMS-mutagenized red-brown mutant had nonsynonymous substitutions that resulted in slightly reduced <i>ANR1</i> activity in vitro. These results suggest that defects in the <i>ANR1</i> gene can be associated with red-brown soybean grain color. These results suggest that suppressing <i>ANR1</i> gene expression or activity may be a rational approach toward engineering seed coat color to enable the visual identification of genetically modified soybean grains