A root-expressed l-phenylalanine:4-hydroxyphenylpyruvate aminotransferase is required for tropane alkaloid biosynthesis in atropa belladonna

Matthew A. Bedewitz, Elsa Góngora-Castillo, Joseph B. Uebler, Eliana Gonzales-Vigil, Krystle E. Wiegert-Rininger, Kevin L. Childs, John P. Hamilton, Brieanne Vaillancourt, Yun Soo Yeo, Joseph Chappell, Dean Penna Della, A. Daniel Jones, C. Robin Buell, Cornelius S. Barry

Research output: Contribution to journalArticlepeer-review

66 Scopus citations

Abstract

The tropane alkaloids, hyoscyamine and scopolamine, are medicinal compounds that are the active components of several therapeutics. Hyoscyamine and scopolamine are synthesized in the roots of specific genera of the Solanaceae in a multistep pathway that is only partially elucidated. To facilitate greater understanding of tropane alkaloid biosynthesis, a de novo transcriptome assembly was developed for Deadly Nightshade (Atropa belladonna). Littorine is a key intermediate in hyoscyamine and scopolamine biosynthesis that is produced by the condensation of tropine and phenyllactic acid. Phenyllactic acid is derived from phenylalanine via its transamination to phenylpyruvate, and mining of the transcriptome identified a phylogenetically distinct aromatic amino acid aminotransferase (ArAT), designated Ab-ArAT4, that is coexpressed with known tropane alkaloid biosynthesis genes in the roots of A. belladonna. Silencing of Ab-ArAT4 disrupted synthesis of hyoscyamine and scopolamine through reduction of phenyllactic acid levels. Recombinant Ab-ArAT4 preferentially catalyzes the first step in phenyllactic acid synthesis, the transamination of phenylalanine to phenylpyruvate. However, rather than utilizing the typical keto-acid cosubstrates, 2-oxoglutarate, pyruvate, and oxaloacetate, Ab-ArAT4 possesses strong substrate preference and highest activity with the aromatic keto-acid, 4-hydroxyphenylpyruvate. Thus, Ab-ArAT4 operates at the interface between primary and specialized metabolism, contributing to both tropane alkaloid biosynthesis and the direct conversion of phenylalanine to tyrosine.

Original languageEnglish
Pages (from-to)3745-3762
Number of pages18
JournalPlant Cell
Volume26
Issue number9
DOIs
StatePublished - Sep 1 2014

Bibliographical note

Publisher Copyright:
© 2014 American Society of Plant Biologists. All rights reserved.

ASJC Scopus subject areas

  • Plant Science

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