Sorghum seed coat color correlates with the accumulation of phenolic and volatile compounds, and key regulatory genes including ABCB28, PTCD1, and ANK have been identified as central to their biosynthesis and transport.

Keywords: Network analysis, Phenolics, R-seq, Seed coat color, Sorghum, Volatile compound

Sorghum (Sorghum bicolor) is a nutritionally and industrially valuable cereal, enriched in phenolic compounds such as tannins, flavonoids, and 3-deoxyanthocyanidins, which contribute to its antioxidant capacity and potential to reduce chronic disease risks. These phenolics, along with diverse volatile organic compounds (VOCs) like alcohols and esters, also influence sorghum’s sensory and fermentation properties. Seed coat color, ranging from white to black, correlates with phenolic concentration, with darker grains typically exhibiting higher tannin and flavonoid contents. Researchers from Korea Atomic Energy Research Institute, Sunchon National University, Chonnam National University and the National Institute of Agricultural Sciences investigated the phenolic and VOC profiles of sorghum lines with varying seed coat colors and confirmed a negative correlation between seed lightness (L*) and total phenolic content (TPC). While seed coat pigmentation is an indirect marker for tannin content, its reliability depends on the presence of the colored testa layer. Red and brown grains showed particularly high a* values (redness), indicating elevated flavonoid content, thus offering potential in breeding sorghum varieties for enhanced functional properties.

To dissect the genetic basis of these traits, weighted gene co-expression network analysis (WGCNA) integrated with RNA-seq was employed across four sorghum genotypes. This approach identified modules associated with phenolic and volatile accumulation, highlighting three hub genes: SbRio.02G135800.1 (ABCB28), SbRio.02G242300.1 (PTCD1), and SbRio.02G265800.1 (ANK). ABCB28, an ATP-binding cassette transporter, likely mediates flavonoid transport and accumulation, influencing both seed coat pigmentation and antioxidant capacity. PTCD1, a PPR domain-containing gene, may indirectly regulate phenolic biosynthesis via mitochondrial energy metabolism. ANK genes, responsive to hormonal signals like ABA and auxin, are implicated in flavonoid pathway regulation. Together, these findings provide molecular targets for sorghum improvement and deepen our understanding of color-linked metabolic diversity in cereal crops.

SorghumBase examples: 

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Figure 1: One of the hub genes the authors identified, SbRio.02G135800.v2.1, was strongly correlated with tannin, phenolic, volatiles, and seed lightness metrics. A) This homology view displays the orthologs of this ABC transporter family genes with generally strong conservation of structure across sorghum accessions. B) However, there is significant neighborhood variation in regards to surrounding gene structure, orientation, and transposable elements that could influence this gene’s activity in other lines.
Figure 2: A variant image view of SbRio.02G135800.v2.1 that displays all the variations in genetic content within natural variant populations. The image is interactable and selecting any variant will generate a pop-up box with additional content about the variant of interest along with a link to more detailed information, like allele frequency, which germplasm contains which allele and plant introductions (PI) numbers so researchers can order accessions for research.

Reference:

Lee YJ, Kim WJ, Lee SH, Kim JH, Kwon SJ, Ahn JW, Kim SH, Kim JB, Lyu JI, Bae CH, Ryu J. Weighted gene co-expression network analysis - based selection of hub genes related to phenolic and volatile compounds and seed coat color in sorghum. BMC Plant Biol. 2025 May 23;25(1):682. PMID: 40410657. doi: 10.1186/s12870-025-06657-w. Read more

Genetic and Metabolic Insights into the Relationship Between Seed Coat Color, Phenolic Compounds, and Volatile Profiles in Sorghum

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