Journal
PLANT CELL
Volume 26, Issue 9, Pages 3745-3762Publisher
OXFORD UNIV PRESS INC
DOI: 10.1105/tpc.114.130534
Keywords
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Funding
- National Institutes of General Medical Sciences [1RC2GM092521]
- Michigan State University (MSU) Foundation Strategic Partnership Grant
- National Science Foundation [IOS-1025636]
- Michigan AgBioResearch and through USDA National Institute of Food and Agriculture [MICL02265, MICL02143]
- Summer Undergraduate Research Fellowship from the American Society of Plant Biologists
- MSU College of Agriculture and Natural Resources Undergraduate Research Program
- MSU Plant Breeding, Genetics, and Biotechnology Graduate Program
- National Science Foundation Major Research Instrumentation Grant [DBI-0619489]
- Division Of Integrative Organismal Systems
- Direct For Biological Sciences [1025636] Funding Source: National Science Foundation
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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.
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