3′O-Methyltransferase, Ps3′OMT, from opium poppy: involvement in papaverine biosynthesis
Using, in silico, in vitro and in planta functional assays, we demonstrate that Ps3′OMT, an 3′-O methyl transferase is linked to papaverine biosynthesis in opium poppy.
Papaverine, one of the benzylisoquinoline alkaloids (BIA) synthesized in the medicinally important plant, Papaver somniferum, is known for the potent pharmacological properties. Papaverine biosynthesis has remained debatable as two different pathways, NH (involving N-desmethylated intermediates) and the NCH3 (involving N-methylated intermediates), have been proposed. In addition, there are several intermediate steps in both the proposed pathways that are not very well characterized in terms of specific enzymes. In this study, we report the identification and functional characterization of 3′O-methyltransferase (Ps3′OMT) which might participate in the 3′O-methylation of the intermediates in the papaverine biosynthesis. Comparison of transcript and metabolite profiles of high and low papaverine producing cultivar revealed the occurrence of a 3′O-methyltransferase, Ps3′OMT, which was abundant in aerial organs and shared 72% identity with the GfLOMT7 predicted to have 3′OMT activity. In silico studies based on homology modeling, docking and MD simulations predicted (S)-norlaudanine as the potential substrate forming a stable complex with Ps3′OMT. Suppression of Ps3′OMT through virus-induced gene silencing resulted in a remarkable decrease in the level of papaverine in comparison to control plants. The characterization of the functionally unique Ps3′OMT involved in BIA metabolism suggests an involvement of the NH pathway leading to papaverine biosynthesis.
KeywordsBenzylisoquinoline alkaloids NH pathway O-Methyltransferase Opium poppy Papaver somniferum Papaverine biosynthesis
Authors are thankful to the Council of Scientific and Industrial Research (CSIR), New Delhi for financial support under Network project (BSC-107). PA, SP as well as RK acknowledge Department of Biotechnology, Government of India and University Grants Commission (UGC) for Senior and Junior Research Fellowships. Authors acknowledge Dr. Surendra Pratap Singh, CSIR-NBRI for help in confocal microscopy.
Author contribution statement
PA, SP, SS and PKT designed the research; PA, RK and AP performed the experiments; YVD carried out the bioinformatics analysis; PA and PKT wrote the paper.
Compliance with ethical standards
Conflict of interest
Authors declare that they have no competing interests. All authors have read and approved the final manuscript.
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