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Systematic silencing of benzylisoquinoline alkaloid biosynthetic genes reveals the major route to papaverine in opium poppy.
- Source :
-
The Plant journal : for cell and molecular biology [Plant J] 2012 Oct; Vol. 72 (2), pp. 331-44. Date of Electronic Publication: 2012 Aug 09. - Publication Year :
- 2012
-
Abstract
- Papaverine, a major benzylisoquinoline alkaloid in opium poppy (Papaver somniferum), is used as a vasodilator and antispasmodic. Conversion of the initial intermediate (S)-norcoclaurine to papaverine involves 3'-hydroxylation, four O-methylations and dehydrogenation. However, our understanding of papaverine biosynthesis remains controversial more than a century after an initial scheme was proposed. In vitro assays and in vivo labeling studies have been insufficient to establish the sequence of conversions, the potential role of the intermediate (S)-reticuline, and the enzymes involved. We used virus-induced gene silencing in opium poppy to individually suppress the expression of six genes with putative roles in papaverine biosynthesis. Suppression of the gene encoding coclaurine N-methyltransferase dramatically increased papaverine levels at the expense of N-methylated alkaloids, indicating that the main biosynthetic route to papaverine proceeds via N-desmethylated compounds rather than through (S)-reticuline. Suppression of genes encoding (S)-3'-hydroxy-N-methylcoclaurine 4-O-methyltransferase and norreticuline 7-O-methyltransferase, which accept certain N-desmethylated alkaloids, reduced papaverine content. In contrast, suppression of genes encoding N-methylcoclaurine 3'-hydroxylase or reticuline 7-O-methyltransferase, which are specific for N-methylated alkaloids, did not affect papaverine levels. Suppression of norcoclaurine 6-O-methyltransferase transcript levels significantly suppressed total alkaloid accumulation, implicating (S)-coclaurine as a key branch-point intermediate. The differential detection of N-desmethylated compounds in response to suppression of specific genes highlights the primary route to papaverine.<br /> (© 2012 The Authors. The Plant Journal © 2012 Blackwell Publishing Ltd.)
- Subjects :
- Benzylisoquinolines metabolism
Biosynthetic Pathways
Cytochrome P-450 Enzyme System genetics
Cytochrome P-450 Enzyme System metabolism
Gene Expression Regulation, Plant
Gene Silencing
Latex isolation & purification
Methyltransferases genetics
Methyltransferases metabolism
Papaver chemistry
Papaver genetics
Papaver metabolism
Papaverine metabolism
Plant Proteins metabolism
Plant Stems chemistry
Plant Stems enzymology
Plant Stems genetics
Plant Stems metabolism
RNA, Messenger genetics
RNA, Plant genetics
Real-Time Polymerase Chain Reaction
Vasodilator Agents metabolism
Alkaloids metabolism
Latex chemistry
Papaver enzymology
Plant Proteins genetics
Subjects
Details
- Language :
- English
- ISSN :
- 1365-313X
- Volume :
- 72
- Issue :
- 2
- Database :
- MEDLINE
- Journal :
- The Plant journal : for cell and molecular biology
- Publication Type :
- Academic Journal
- Accession number :
- 22725256
- Full Text :
- https://doi.org/10.1111/j.1365-313X.2012.05084.x