Phenotypic, phytochemical, and transcriptomic analysis of black sorghum (Sorghum bicolor L.) pericarp in response to light quality

Authors: FEDENIA, LAUREN - Texas A&M University; Klein, Robert - Bob; Dykes, Linda; ROONEY, WILLIAM - Texas A&M University; KLEIN, PATRICIA - Texas A&M University

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2020
Publication Date: 8/21/2020
Citation: Fedenia, L., Klein, R.R., Dykes, L., Rooney, W., Klein, P. 2020. Phenotypic, phytochemical, and transcriptomic analysis of black sorghum (Sorghum bicolor L.) pericarp in response to light quality. Journal of Agricultural and Food Chemistry. 68:9917-9929. https://doi.org/10.1021/acs.jafc.0c02657.
DOI: https://doi.org/10.1021/acs.jafc.0c02657

Interpretive Summary: The black grain trait in sorghum has notable value in the specialty food and nutraceutical industries. The black coloration of the grain is associated with a group of rare compounds valued for use as natural food colorants, food preservatives, antioxidant food additives, and as compounds cytotoxic to cancer cells. In the present study, we found that UV light is critical for the black coloration of the grain and for the associated accumulation of health-associated compounds in the seed. Based on the unique upregulation of a suite of genes in black seed, we postulate that UV light produces a stress in black sorghum grain tissue, which triggers the seed to turn black providing a sunscreen to the harmful effects of UV light. This study is critical for breeders and sorghum growers to pick the best environment for growing the blackest sorghum with the highest level of the health-associated compounds in the black seed.

Technical Abstract: Black sorghum [Sorghum bicolor (L.) Moench] is characterized by the black appearance of the pericarp and production of 3-deoxyanthocyanidins (3-DOA), which are valued for their cytotoxicity to cancer cells and as natural food colorants and antioxidant additives. The black pericarp phenotype is not fully penetrant in all environments, which implicates the light spectrum and/or photoperiod as critical factors for trait expression. In this study, black- or red-pericarp genotypes were grown under light regimes of visible light, visible supplemented with UVA or supplemented with UVA plus UVB (or dark control). Pericarp 3-DOAs and pericarp pigmentation were maximized in the black genotype exposed to a light regime with UVB. Changes in gene expression during black pericarp development revealed that UV light activates genes relating to plant defense, reactive oxygen species and secondary metabolism suggesting that 3-DOA accumulation is associated with activation of flavonoid biosynthesis and several overlapping defense and stress signaling pathways.