TY - BOOK
T1 - Investigation of regulation and transport of barley hydroxynitrile glucosides
AU - Ehlert, Marcus
PY - 2018
Y1 - 2018
N2 - Hydroxynitrile glucosides are a group of bioactive secondary metabolites involved in plant defence against pests and diseases. Many hydroxynitrile glucosides are cyanogenic and liberate toxic hydrogen cyanide after contact with specific β-glucosidases. Under normal conditions, both components are spatially separated to prevent autotoxic effects, and the reaction is only induced by mechanical tissue disruption. Cyanogenic α-hydroxynitrile glucosides often co-occur with non-cyanogenic β- and γ-hydroxynitrile glucosides, which are also suggested to function in defence. The compounds are present in a high number of food plants, such as barley, cassava and sorghum. Barley produces five hydroxynitrile glucosides, including the cyanogenic glucoside epiheterodendrin, which was identified as source of carcinogenic ethyl carbamate formation during distillation processes. In Scotch whisky production, this contaminant is controlled by the use of cultivars with low hydroxynitrile glucoside contents. This strategy raises a demand to breed against the compounds, which comes with the risk to lose their otherwise beneficial functions in defence. Bioengineering approaches could help to selectively control the content of epiheterodendrin, and useful targets of such approaches are e.g. the transporters required for the distribution of the compounds or the factors regulating biosynthesis. One transporter of the ABC and one of the MATE family are located next to the biosynthetic gene cluster for hydroxynitrile glucosides in barley, and their involvement in the transport is investigated. Phylogenetic and functional comparison of both transporter families in barley to members in other dicot and monocot species provides new insights into the evolution of the specific subfamilies in plants, and identifies orthologs in barley that are potentially involved in secondary metabolite transport and stress resistance. In addition to the transporter studies, cultivar-specific variations in the total hydroxynitrile glucoside content are investigated on the genomic level, and revealed a major deletion in the genomic cluster and transcriptional regulation of the biosynthetic genes as the causes. The data contribute to future experiments aiming the identification of the factors regulating gene expression. The expression of the biosynthetic genes is also investigated in barley leaves infected with the barley powdery mildew fungus Blumeria graminis f.sp. hordei in order to study the involvement of hydroxynitrile glucosides in this interaction. In agreement with previous studies on the metabolite level, the data support an involvement of the compounds in the interaction, and once again raise the question whether the compounds are useful for the plant or the fungus.
AB - Hydroxynitrile glucosides are a group of bioactive secondary metabolites involved in plant defence against pests and diseases. Many hydroxynitrile glucosides are cyanogenic and liberate toxic hydrogen cyanide after contact with specific β-glucosidases. Under normal conditions, both components are spatially separated to prevent autotoxic effects, and the reaction is only induced by mechanical tissue disruption. Cyanogenic α-hydroxynitrile glucosides often co-occur with non-cyanogenic β- and γ-hydroxynitrile glucosides, which are also suggested to function in defence. The compounds are present in a high number of food plants, such as barley, cassava and sorghum. Barley produces five hydroxynitrile glucosides, including the cyanogenic glucoside epiheterodendrin, which was identified as source of carcinogenic ethyl carbamate formation during distillation processes. In Scotch whisky production, this contaminant is controlled by the use of cultivars with low hydroxynitrile glucoside contents. This strategy raises a demand to breed against the compounds, which comes with the risk to lose their otherwise beneficial functions in defence. Bioengineering approaches could help to selectively control the content of epiheterodendrin, and useful targets of such approaches are e.g. the transporters required for the distribution of the compounds or the factors regulating biosynthesis. One transporter of the ABC and one of the MATE family are located next to the biosynthetic gene cluster for hydroxynitrile glucosides in barley, and their involvement in the transport is investigated. Phylogenetic and functional comparison of both transporter families in barley to members in other dicot and monocot species provides new insights into the evolution of the specific subfamilies in plants, and identifies orthologs in barley that are potentially involved in secondary metabolite transport and stress resistance. In addition to the transporter studies, cultivar-specific variations in the total hydroxynitrile glucoside content are investigated on the genomic level, and revealed a major deletion in the genomic cluster and transcriptional regulation of the biosynthetic genes as the causes. The data contribute to future experiments aiming the identification of the factors regulating gene expression. The expression of the biosynthetic genes is also investigated in barley leaves infected with the barley powdery mildew fungus Blumeria graminis f.sp. hordei in order to study the involvement of hydroxynitrile glucosides in this interaction. In agreement with previous studies on the metabolite level, the data support an involvement of the compounds in the interaction, and once again raise the question whether the compounds are useful for the plant or the fungus.
UR - https://rex.kb.dk/primo-explore/fulldisplay?docid=KGL01012010740&context=L&vid=NUI&search_scope=KGL&tab=default_tab&lang=da_DK
M3 - Ph.D. thesis
BT - Investigation of regulation and transport of barley hydroxynitrile glucosides
PB - Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen
ER -