Biosynthesis of the leucine derived α‐, β‐ and γ‐hydroxynitrile glucosides in barley (Hordeum vulgare L.) |
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Authors: | Mohammed Saddik Motawie Carl Erik Olsen Birger Lindberg Møller Michael Foged Lyngkjær |
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Institution: | 1. Department of Plant and Environmental Sciences, Plant Biochemistry Laboratory, University of Copenhagen, Copenhagen, Denmark;2. VILLUM Research Center for Plant Plasticity, University of Copenhagen, Copenhagen, Denmark;3. Carlsberg Laboratory, Copenhagen V, Denmark |
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Abstract: | Barley (Hordeum vulgare L.) produces five leucine‐derived hydroxynitrile glucosides (HNGs), of which only epiheterodendrin is a cyanogenic glucoside. The four non‐cyanogenic HNGs are the β‐HNG epidermin and the γ‐HNGs osmaronin, dihydroosmaronin and sutherlandin. By analyzing 247 spring barley lines including landraces and old and modern cultivars, we demonstrated that the HNG level varies notably between lines whereas the overall ratio between the compounds is constant. Based on sequence similarity to the sorghum (Sorghum bicolor) genes involved in dhurrin biosynthesis, we identified a gene cluster on barley chromosome 1 putatively harboring genes that encode enzymes in HNG biosynthesis. Candidate genes were functionally characterized by transient expression in Nicotiana benthamiana. Five multifunctional P450s, including two CYP79 family enzymes and three CYP71 family enzymes, and a single UDP‐glucosyltransferase were found to catalyze the reactions required for biosynthesis of all five barley HNGs. Two of the CYP71 enzymes needed to be co‐expressed for the last hydroxylation step in sutherlandin synthesis to proceed. This observation, together with the constant ratio between the different HNGs, suggested that HNG synthesis in barley is organized within a single multi‐enzyme complex. |
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Keywords: | Hordeum vulgare hydroxynitrile glucoside content hydroxynitrile glucoside ratios multifunctional P450s CYP79A12 CYP79A8 CYP71C113 CYP71L1 UGT85F22 oxime toxicity |
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