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

Abstract

Dhurrin [(S)‐p‐hydroxymandelonitrile‐β‐D‐glucopyranoside] 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.

Amylopectin Chain Length Dynamics and Activity Signatures of Key Carbon Metabolic Enzymes Highlight Early Maturation as Culprit for Yield Reduction of Barley Endosperm Starch after Heat Stress

“…Consequently, the most promising strategy to improve the performance of cereal crop plants under thermal stress appears to be source related, namely the introduction of functional stay-green traits that prevent precocious senescence. In sorghum, stay green has for instance been associated with the formation and presence of the cyanogenic glucoside dhurrin (Hayes et�al. 2015, Emendack et�al.…”

An integrated and comparative approach towards identification, characterization and functional annotation of candidate genes for drought tolerance in sorghum (Sorghum bicolor (L.) Moench)

“…It was shown that sorghum dhurrin content in leaf tissue is controlled by genes involved the biosynthetic and catabolic pathways in different level of Nitrogen [ 54 ]. It was also reported that there is association between high leaf dhurrin content and expression of the stay-green trait [ 55 ]. An enzyme CYP79A1 [EC:1.14.13.41] that is grouped into a class of oxidoreductases and encoded by a putatively uncharacterised hypothetical protein gene ‘Sb01g001200’ was identified with a direct involvement in drought tolerance, as it was recently known to be aligned with dhurrin QTL that is associated with stay-green trait [ 55 ].…”

“…It was also reported that there is association between high leaf dhurrin content and expression of the stay-green trait [ 55 ]. An enzyme CYP79A1 [EC:1.14.13.41] that is grouped into a class of oxidoreductases and encoded by a putatively uncharacterised hypothetical protein gene ‘Sb01g001200’ was identified with a direct involvement in drought tolerance, as it was recently known to be aligned with dhurrin QTL that is associated with stay-green trait [ 55 ]. A transcriptional regulation of this enzyme largely determines the synthesis of dhurrin, based on the developmental stage and growth condition of sorghum [ 53 , 56 ].…”

Early Seedling Growth Characteristics Relate to the Staygreen Trait and Dhurrin Levels in Sorghum

“…Categorization of materials into dhurrin levels, rather than dhurrin contents, was based on the fact that, while values for dhurrin contents varied with the different locations, high dhurrin-level lines always showed higher dhurrin content than low dhurrin-level lines in all locations used for evaluations by Burke et al (2013) and Hayes et al (2016). Sorghum materials used had known dhurrin levels (high or low), based on multiyear and multilocation assessments of dhurrin contents from leaves of plants at the late vegetative stage.…”

“…Sorghum materials used had known dhurrin levels (high or low), based on multiyear and multilocation assessments of dhurrin contents from leaves of plants at the late vegetative stage. Categorization of materials into dhurrin levels, rather than dhurrin contents, was based on the fact that, while values for dhurrin contents varied with the different locations, high dhurrin-level lines always showed higher dhurrin content than low dhurrin-level lines in all locations used for evaluations by Burke et al (2013) and Hayes et al (2016). The germplasm used in this study came from the Cropping System Research Laboratory sorghum-breeding program at USDA-ARS, Lubbock, and included sorghum conversion lines, recombinant inbred lines (RILs, from a cross between staygreen BTx642 and senescence TX7000), a BTx623 EMS-induced F 2 mutant population, and breeding lines commonly used in sorghum breeding programs (Table 1).…”