Cyanogenesis in the Sorghum Genus: From Genotype to Phenotype

Abstract

Domestication has resulted in a loss of genetic diversity in our major food crops, leading to susceptibility to biotic and abiotic stresses linked with climate change. Crop wild relatives (CWR) may provide a source of novel genes potentially important for re-gaining climate resilience. Sorghum bicolor is an important cereal crop with wild relatives that are endemic to Australia. Sorghum bicolor is cyanogenic, but the cyanogenic status of wild Sorghum species is not well known. In this study, leaves of wild species endemic in Australia are screened for the presence of the cyanogenic glucoside dhurrin. The direct measurement of dhurrin content and the potential for dhurrin-derived HCN release (HCNp) showed that all the tested Australian wild species were essentially phenotypically acyanogenic. The unexpected low dhurrin content may reflect the variable and generally nutrient-poor environments in which they are growing in nature. Genome sequencing of six CWR and PCR amplification of the CYP79A1 gene from additional species showed that a high conservation of key amino acids is required for correct protein function and dhurrin synthesis, pointing to the transcriptional regulation of the cyanogenic phenotype in wild sorghum as previously shown in elite sorghum.

Regulation of cyanogenic glucosides in wild and domesticated Eusorghum taxa

“…verticilliflorum, we have identified two wild Sorghum taxa that break this trend, more closely matching the CNglc regulation patterns of domesticated sorghum. High HCN potential (~0.7 mg g À1 ) had previously been detected in mature S. propinquum leaves by Cowan et al (2022), supporting our result. Sorghum bicolor subsp.…”

“…High HCN potential (~0.7 mg g −1 ) had previously been detected in mature S. propinquum leaves by Cowan et al . ( 2022 ), supporting our result. Sorghum bicolor subsp.…”

“…Sorghum Moench is a genus of Poaceae whose members produce the CNglc dhurrin. Every Sorghum taxon tested thus far has the ability to produce and store dhurrin, but HCN potential greatly differs between organs and species (Cowan et al 2022). Domesticated sorghum (Sorghum bicolor [L.] Moench subsp.…”

Transcript profiles of wild and domesticated sorghum under water-stressed conditions and the differential impact on dhurrin metabolism

“…The dhurrin levels in the leaves of S. macrospermum was 1000-fold lower than in the leaves of S. bicolor, while water-stress did not significantly increase the leaf dhurrin levels of S. macrospermum . Another recent study (Cowan et al 2022 ) supports these findings showing that the leaf dhurrin content of wild sorghum species are significantly lower than those in S. bicolor . However, the dhurrin levels in the roots of wild sorghum species are similar to the levels in the domesticated S. bicolor (Cowan et al 2021 ).…”

“…Although, cultivated sorghum plants use cyanogenesis as an herbivore defence mechanism, wild sorghum leaves might have roles other than defence. S. macrospermum is endemic to northern Australia, and the low nitrogen availability of the soil (Dillon et al 2007 ) in their habitat, might result in the available nitrogen being utilized in general metabolic and growth process rather than cyanogenesis also, dhurrin may be instantly converted into free nitrogen (Cowan et al 2022 ). Therefore, wild sorghum species have low dhurrin content in the leaves and the plants might rely on other defence mechanisms such as trichomes on the leaf surface (Johnson 1975 ).…”