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The bifurcation of the cyanogenic glucoside and glucosinolate biosynthetic pathways
Author(s) -
Clausen Mette,
Kannangara Rubini M.,
Olsen Carl E.,
Blomstedt Cecilia K.,
Gleadow Roslyn M.,
Jørgensen Kirsten,
Bak Søren,
Motawie Mohammed S.,
Møller Birger Lindberg
Publication year - 2015
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.13023
Subject(s) - glucosinolate , nicotiana benthamiana , arabidopsis thaliana , glucoside , stereochemistry , biosynthesis , enzyme , mutant , oxime , chemistry , biology , biochemistry , botany , medicine , alternative medicine , pathology , gene , brassica
Summary 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 CYP 79A1 catalyzes conversion of tyrosine to ( E ) ‐p ‐hydroxyphenylacetaldoxime whereas CYP 71E1 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 CYP 79 family enzyme, but the next enzyme involved belongs to the CYP 83 family. We demonstrate that CYP 83B1 from Arabidopsis thaliana cannot convert the ( E )‐ p ‐hydroxyphenylacetaldoxime to the ( Z )‐isomer, which blocks the route towards cyanogenic glucoside synthesis. Instead CYP 83B1 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 CYP 79‐derived E‐oximes may play an important role in plant defense.