Identification and Fine Mapping of a MYB-like Transcription Factor Regulating Yellow Grain in Sorghum bicolor

Sorghum is an important raw material for China's baijiu (liquor) brewing industry, and the tannin content in its grains directly affects the quality and nutritional value of the liquor. Grain color is closely associated with tannin content, yet the genetic mechanism underlying grain color formation remains incompletely understood. In this study, we systematically observed grain development in the yellow-grained sorghum line GW605. The results showed that from 1 to 16 days after flowering (DAF), the grains underwent a rapid growth phase, after which the expansion rate slowed. On 25 DAF, the green color of the grains gradually faded, shifting from white to yellow and continuously deepening, ultimately turning dark yellow. A segregating population was subsequently constructed using GW605 (yellow grain) and 6E16 (white grain) as parents. Bulked segregant analysis (BSA) localized the gene controlling the yellow grain to chromosome 1. Through fine mapping based on recombinant individuals, the gene was narrowed to a 108 kb physical interval containing seven candidate genes. Sequencing and functional annotation of the candidate genes suggested that Yellow Seed 2 (Sobic.001G397900) is the candidate gene associated with yellow grain color difference between the two parental lines. Haplotype analysis of Yellow Seed 2 using resequencing data from 698 sorghum germplasm accessions detected a total of 11 SNP loci, forming four haplotypes, among which Hap1 was the predominant haplotype. Further analysis revealed that the haplotype diversity of Yellow Seed 2 increased considerably during the domestication process from Chinese landraces to Chinese cultivars, suggesting that this gene may have incorporated genetic lineages from foreign germplasm during domestication.