The bifurcation of the cyanogenic glucoside and glucosinolate biosynthetic pathways

Mette Clausen, Rubini Maya Kannangara, Carl Erik Olsen, Cecilia Karstin Moni Maria Blomstedt, Roslyn M Gleadow, Kirsten Jorgensen, Soren Bak, Mohammed Saddik Motawie, Birger Lindberg Moller

Research output: Contribution to journalArticleResearchpeer-review

19 Citations (Scopus)

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.
Original languageEnglish
Pages (from-to)558-573
Number of pages16
JournalThe Plant Journal
Volume84
Issue number3
DOIs
Publication statusPublished - 2015

Keywords

  • E- and Z-oxime metabolism
  • oxime dehydration
  • nitriles
  • microbial Z-oxime-nitrile pathway
  • cytochrome P450, CYP79A1
  • CYP71E1
  • CYP83B1
  • Sorghum bicolor
  • Sinapis alba

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