| dc.description.abstract | Sorghum [Sorghum bicolor (L.) Moench] is a major cereal crop grown for feed, silage, and human consumption. Specialty grain-types are typically red, yellow, or white and this coloration is associated with specific polyphenol profiles that serve as an important dietary source of diverse plant polyphenols. Unique amongst the common grain sorghums are the black grain genotypes that are all descendants of the accession ‘Black Shawaya’ from the Sudan. The black pigmentation of ‘Black Shawaya’ grain is associated with the accumulation of rare polyphenols, 3-deoxyanthocyanidins (3-DOAs), however, the expression of this trait is not observed in all environments conducive to grain sorghum production. The present research aimed to elucidate the environmental factors required for full penetrance of this trait and the distinct genetic pathways that condition the atypical accumulation of 3-DOA in the black sorghum pericarp.
Light spectrum and/or photoperiod were previously implicated as critical factors for the expression of this trait. In this research, the black sorghum genotype was grown under regimes of visible light, visible light 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 supplemented with UVB revealing that a fluence of UVB is the determining environmental component for trait penetrance.
Multiple trait mapping methodologies were used to characterize the genomic loci associated with the black sorghum phenotype including genetic linkage map construction with quantitative trait loci (QTL) analysis using an F5 recombinant inbred line population segregating for pericarp 3-DOA accumulation and bulked segregant analysis (BSA) of opposing phenotypic extremes for 3-DOA accumulation. Four major overlapping QTL were detected in multiple mapping efforts along with several minor-effect QTL discovered in separate mapping methods. These mapping efforts revealed genomic regions of the sorghum genome controlling this trait and provided the foundation for additional elucidation of genes regulating the cascade of cellular events leading to the black pericarp phenotype.
Finally, a detailed transcriptome and co-expression analysis performed on pericarp, leaf, and root tissue from black- and red-grain sorghum genotypes under different light regimes revealed a potential metabolic and signaling pathway modeling 3-DOA induction in black sorghum pericarp tissue in which UVB triggers the generation of endogenous elicitors that initiate a signal cascade resulting in the high expression of flavonoid biosynthetic genes ultimately responsible for 3-DOA synthesis. | en |
