Regulation of cyanogenic glucosides in wild and domesticated Eusorghum taxa

Abstract

Domesticated sorghum (Sorghum bicolor [L.] Moench subsp. bicolor) diverts significant amounts of nitrogen away from primary metabolism to the synthesis of cyanogenic glucosides (CNglc)specialized metabolites that release toxic hydrogen cyanide (HCN). Our aim was to identify the point in the genus Sorghum Moench at which plants gained the ability to maintain hazardous concentrations of cyanogenic glucosides in their leaves into maturity (HCN potential >0.4 mg g À1 ). This ability occurs in domesticated sorghum (in the subgenus Eusorghum), but not in wild taxa in other Sorghum subgenera.• Eight accessions from the subgenus Eusorghum were grown in a common garden: an improved sorghum line, five sorghum landraces, the crop's wild progenitor (S. bicolor subsp. verticilliflorum [Steud.] de Wet ex Wiersema & J. Dahlb.) and wild Sorghum propinquum (Kunth) Hitchc. HCN potential was measured in plants (n = 80) at the three-leaf stage and at 6 weeks old.• All study accessions, including the wild taxa, had hazardous CNglc concentrations in the leaves at both the three-leaf stage (mean HCN potentials > = 2.5 mg g À1 ) and at 6 weeks old (mean HCN potentials > = 0.68 mg g À1 ), greatly contrasting the much lower mature leaf HCN potentials previously found in wild Sorghum taxa outside subgenus Eusorghum (generally <= 0.01 mg g À1 ).• Our results suggest that the ability to maintain hazardous leaf HCN potentials into maturity might have arisen during the divergence of Eusorghum from other Sorghum subgenera, rather than during the speciation or domestication of S. bicolor, and highlights the value of utilizing Sorghum taxa outside Eusorghum in efforts to improve the crop safety of sorghum.

Phenotypic and genotypic variation in Australian native Sorghum species along aridity clines

“…Lazarides et al (1991) conducted a comprehensive ecological survey; however, since then, much of the research into wild sorghums has focused on single accessions within species (e.g. Cowan et al 2020;Myrans et al 2021;Cowan et al 2022;Myrans and Gleadow 2022). This is largely due to the difficulty of obtaining seed from the remote areas in which they are found.…”

“…Although CNglcs remain useful in defence against herbivory, the major roles of CNglcs in wild sorghums are unresolved. When mature, wild sorghums typically have very low HCN potential in their leaves (<10 μg g −1 ), and higher HCN potential in their roots (0-750 μg g −1 ) (Myrans and Gleadow 2022). The storage of CNglcs at such low concentrations, and away from the tissues most vulnerable to herbivore damage, makes wild sorghums attractive sources of genes for improving forage sorghums, which often have toxic leaf HCN potentials (Cowan et al 2020).…”