The bifurcation of the cyanogenic glucoside and glucosinolate biosynthetic pathways.

Abstract

The biosynthetic pathway for the cyanogenic glucoside dhurrin in sorghum has previously been shown to involve the sequential production of (E)- and (Z)-p-hydroxyphenylacetaldoxime. In this study we used microsomes prepared from wild-type and mutant sorghum or transiently transformed Nicotiana benthamiana to demonstrate that CYP79A1 catalyzes conversion of tyrosine to (E)-p-hydroxyphenylacetaldoxime whereas CYP71E1 catalyzes conversion of (E)-p-hydroxyphenylacetaldoxime into the corresponding geometrical Z-isomer as required for its dehydration into a nitrile, the next intermediate in cyanogenic glucoside synthesis. Glucosinolate biosynthesis is also initiated by the action of a CYP79 family enzyme, but the next enzyme involved belongs to the CYP83 family. We demonstrate that CYP83B1 from Arabidopsis thaliana cannot convert the (E)-p-hydroxyphenylacetaldoxime to the (Z)-isomer, which blocks the route towards cyanogenic glucoside synthesis. Instead CYP83B1 catalyzes the conversion of the (E)-p-hydroxyphenylacetaldoxime into an S-alkyl-thiohydroximate with retention of the configuration of the E-oxime intermediate in the final glucosinolate core structure. Numerous microbial plant pathogens are able to detoxify Z-oximes but not E-oximes. The CYP79-derived E-oximes may play an important role in plant defense.

• Authors: Mette Clausen, Rubini M Kannangara, Carl E Olsen, Cecilia K Blomstedt, Roslyn M Gleadow, Kirsten Jørgensen, Søren Bak, Mohammed S Motawie, Birger Lindberg Møller
• Journal: The Plant journal : for cell and molecular biology (Plant J) Vol. 84 Issue 3 Pg. 558-73 (Nov 2015) ISSN: 1365-313X [Electronic] England
• PMID: 26361733 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2015 The Authors The Plant Journal © 2015 John Wiley & Sons Ltd.

Chemical References

• Arabidopsis Proteins
• Glucosinolates
• Oximes
• Plant Proteins
• 4-hydroxyphenylacetaldoxime
• Tyrosine
• Cytochrome P-450 Enzyme System
• CYP83B1 protein, Arabidopsis
• cytochrome P450TYR
• cytochrome P-450 CYP71E1 (sorghum)

Topics

• Arabidopsis Proteins (genetics, metabolism)
• Biosynthetic Pathways
• Cytochrome P-450 Enzyme System (genetics, metabolism)
• Glucosinolates (metabolism)
• Isomerism
• Mutation
• Oximes (metabolism)
• Plant Proteins (genetics, metabolism)
• Plants, Genetically Modified
• Sorghum (genetics, metabolism)
• Tobacco (genetics, metabolism)
• Tyrosine (metabolism)