Biosynthesis of the leucine derived α-, β- and γ-hydroxynitrile glucosides in barley (Hordeum vulgare L.)

TY - JOUR

T1 - Biosynthesis of the leucine derived α-, β- and γ-hydroxynitrile glucosides in barley (Hordeum vulgare L.)

AU - Knoch, Eva

AU - Motawie, Mohammed Saddik

AU - Olsen, Carl Erik

AU - Møller, Birger Lindberg

AU - Lyngkjær, Michael Foged

N1 - © 2016 The Authors The Plant Journal © 2016 John Wiley & Sons Ltd.

PY - 2016/10/1

Y1 - 2016/10/1

N2 - 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.

AB - 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.

U2 - 10.1111/tpj.13247

DO - 10.1111/tpj.13247

M3 - Journal article

C2 - 27337134

SN - 0960-7412

VL - 88

SP - 247

EP - 256

JO - Plant Journal

JF - Plant Journal

IS - 2

ER -