Discovery of a Dhurrin QTL in Sorghum: Co-localization of Dhurrin Biosynthesis and a Novel Stay-green QTL

Dhurrin [(S)-p-hydroxymandelonitrile-beta-D-gluco-pyranoside] is a cyanogenic glucoside produced by sorghum (Sorghum bicolor L. Moench) and is generally considered a natural defense compound capable of producing the toxin hydrogen cyanide (HCN) to deter animal herbivory. Recently, high levels of leaf dhurrin have been found in grain sorghum genotypes that also exhibit stay-green during postanthesis water deficit. Post-flowering drought tolerance (stay-green) in sorghum is an economically important trait in sorghum production regions where drought stress postanthesis is common. Stay-green is associated with reduced lodging, charcoal rot resistance, increased grain fill, and increased grain yield. The genetic control of stay-green is complex, with multiple quantitative trait loci (QTL) being identified in affecting expression of stay-grain. Here we report the discovery of a dhurrin QTL (Dhu1) on SBI01 using a recombinant inbred line (RIL) mapping population derived from BTx642/Tx7000. Leaf dhurrin was highly heritable and Dhu1 explained a large percentage of the variation of leaf dhurrin in the population. Dhu1 is aligned with genes involved in dhurrin biosynthesis (CYP79A1, CYP71E1, UGT85B1). Protein sequence variants found in CYP71E1 and UGT85B1 could be the cause of the observed differences in leaf dhurrin levels in BTx642, Tx7000, and other sorghum lines that vary in leaf dhurrin content. Dhu1 is also aligned with a previously un-identified stay-green QTL (Stg5) on SBI01, consistent with prior studies showing an association between high leaf dhurrin levels, this region of SBI01, and expression of the stay-green trait.