A single nucleotide mutation in the fourth exon of RBH1 is responsible for brown hull phenotype in rice.

As one of the important traits, hull color is the morphological marker of rice, which plays an important role in the mechanized color selection of hybrid rice seed production but lacks good application. Here, we obtained a reddish-brown hull 1 (rbh1) mutant from an Indica maintainer material H9808 by aerospace mutagenesi. In the rbh1 mutant, the hull color was reddish brown, and the grain width and 1000-grain weight decreased significantly, but the other agronomic traits did not change significantly. Furthermore, the total flavonoids and anthocyanin content in the rbh1 hulls deposition was remarkably higher than WT, and the lignin level in the rbh1 hull was reduced. Genetic analysis indicated that the reddish-brown hull trait was controlled by a pair of recessive nuclear genes. Map-based cloning indicated that RBH1 was located within the physical distance of 48 kb on the short arm of chromosome 2. The comparative analysis of genome DNA sequence between rbh1 and WT found that a substitution from T to C (+ 1001) occurred in the fourth exon of LOC_Os02g09490 in rbh1 mutant. Genetic complementation experiments indicate that RBH1 is an allele of the previously reported GH2, which encoding a cinnamyl alcohol dehydrogenase protein involving in lignin biosynthesis. qRT-PCR showed that the relative expression of lignin and flavonoid-related genes in the hulls of rbh1 mutant was significantly upregulated, confirming that GH2/RBH1 is an important gene in the metabolism of lignin and flavonoids; and provides material basis for further studying the mechanism of GH2/RBH1 regulating the rice hull color.. In addition, the hybrid F1 combination analysis indicated that the rbh1 mutation site did not affect the agronomic traits and yield of the hybrid rice, which was to cultivate the rbh1 locus into a new sterile line or restorer line with reddish-brown hulls and rice breeding application of rbh1 locus on mechanized seed production of hybrid rice provides a theoretical basis. [ABSTRACT FROM AUTHOR]