Cyanogenesis in the Sorghum Genus: From Genotype to Phenotype.

Max Cowan,Christoph Crocoll,Agnelo Furtado,Cecilia Blomstedt,Camilla Knudsen,Robert Henry,Roslyn M Gleadow,Sally Norton,Birger Lindberg Møller

doi:10.3390/genes13010140

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.

Highlights

Sorghum (Sorghum bicolor (L.) Moench) is a major cereal crop and the fifth most important cereal crop worldwide
Hydrogen cyanide potential (HCNp), as a proxy for cyanogenic glucoside concentration, was determined for leaf tissue harvested from S. bicolor and 18 related Sorghum species
Foliar hydrogen cyanide potential (HCNp) was extremely low in all wild species from the Chaetosorghum, Heterosorghum, Parasorghum and Stiposorghum subgenera compared with the three Eusorghum species at 2, 4, and 6 weeks post-germination (p < 0.001)

Summary

Introduction

Sorghum (Sorghum bicolor (L.) Moench) is a major cereal crop and the fifth most important cereal crop worldwide. As a C4 plant, sorghum has several advantages over wheat and rice under harsh growing conditions as a result of increased photosynthetic efficiency and a higher tolerance to drought and elevated temperatures [1,2]. Sorghum produces the cyanogenic glucoside dhurrin in all vegetative tissues. Cyanogenesis describes the process whereby cyanogenic glucosides are hydrolyzed by specific β-glucosidases to release hydrogen cyanide (HCN) [3]. Plants avoid autotoxicity by the spatial separation of cyanogenic substrate and enzyme at the cellular or subcellular level, HCN is only released following tissue disruption [3–5]. This binary system has been demonstrated to provide plants with an immediate targeted response to herbivore attacks [6–9]. Cyanogenesis limits the use of sorghum as livestock feed and forage [10]

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Discussion

Conclusion