Phenylpropanoid derived flavonoid biosynthesis pathway compensates for abiotic and biotic stress tolerance in dhurrin-free forage sorghum

Abstract

Sorghum (Sorghum bicolor L. Moench) is a multipurpose cereal valued for its drought tolerance and biomass productivity. Despite its agronomic advantages, the widespread adoption of sorghum as a forage crop is significantly limited by the presence of dhurrin, a cyanogenic glucoside that, upon stress or herbivory, releases hydrogen cyanide (HCN), posing considerable risks to grazing animals. This study systematically investigated the metabolic ramifications of dhurrin elimination in a prussic acid-free (PF) sorghum genotype cultivated under contrasting irrigation regimes. The major aim was to elucidate the consequences of the loss of cyanogenesis on both agronomic performance and the modulation of stress-associated metabolic pathways. Untargeted metabolomics using UHPLC-QTOF-MS revealed significant metabolic reprogramming in PF sorghum, with comparable biomass and no yield penalty. Over 470 metabolites were differentially accumulated, including reduced alkaloids and phenolic acids and increased flavonoids, terpenoids, and jasmonates. Metabolic flux was redirected from dhurrin synthesis toward 4-coumarate-derived phenylpropanoid and flavonoid pathways, boosting antioxidant production. Upregulated jasmonic acid biosynthesis suggests activation of alternative defence signalling. The loss of dhurrin leads to a comprehensive specialization of metabolism favoring antioxidant and hormone pathways without compromising growth, providing key insights for developing safer, resilient prussic acid-free forage sorghum.