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Biosynthesis of the leucine derived α‐, β‐ and γ‐hydroxynitrile glucosides in barley ( Hordeum vulgare L.)
Author(s) -
Knoch Eva,
Motawie Mohammed Saddik,
Olsen Carl Erik,
Møller Birger Lindberg,
Lyngkjær Michael Foged
Publication year - 2016
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.13247
Subject(s) - hordeum vulgare , biosynthesis , biochemistry , biology , gene , enzyme , glucosyltransferase , nicotiana benthamiana , hydroxylation , leucine , amino acid , botany , poaceae
Summary Barley ( Hordeum vulgare L.) produces five leucine‐derived hydroxynitrile glucosides ( HNG s), of which only epiheterodendrin is a cyanogenic glucoside. The four non‐cyanogenic HNG s are the β‐ HNG epidermin and the γ‐ HNG s 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 CYP 79 family enzymes and three CYP 71 family enzymes, and a single UDP ‐glucosyltransferase were found to catalyze the reactions required for biosynthesis of all five barley HNG s. Two of the CYP 71 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 HNG s, suggested that HNG synthesis in barley is organized within a single multi‐enzyme complex.