Characterization of benzylisoquinoline alkaloid methyltransferases in Liriodendron chinense provides insights into the phylogenic basis of angiosperm alkaloid diversity
SUMMARY Benzylisoquinoline alkaloids (BIAs) are a class of plant secondary metabolites with great pharmacological value. Their biosynthetic pathways have been extensively elucidated in the species from the Ranunculales order, such as poppy and Coptis japonica, in which methylation events play centra...
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Veröffentlicht in: | The Plant journal : for cell and molecular biology 2022-10, Vol.112 (2), p.535-548 |
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Zusammenfassung: | SUMMARY
Benzylisoquinoline alkaloids (BIAs) are a class of plant secondary metabolites with great pharmacological value. Their biosynthetic pathways have been extensively elucidated in the species from the Ranunculales order, such as poppy and Coptis japonica, in which methylation events play central roles and are directly responsible for BIA chemodiversity. Here, we combined BIA quantitative profiling and transcriptomic analyses to identify novel BIA methyltransferases (MTs) from Liriodendron chinense, a basal angiosperm plant. We identified an N‐methyltransferase (LcNMT1) and two O‐methyltransferases (LcOMT1 and LcOMT3), and characterized their biochemical functions in vitro. LcNMT1 methylates (S)‐coclaurine to produce mono‐ and dimethylated products. Mutagenesis experiments revealed that a single‐residue alteration is sufficient to change its substrate selectivity. LcOMT1 methylates (S)‐norcoclaurine at the C6 site and LcOMT3 methylates (S)‐coclaurine at the C7 site, respectively. Two key residues of LcOMT3, A115 and T301, are identified as important contributors to its catalytic activity. Compared with Ranunculales‐derived NMTs, Magnoliales‐derived NMTs were less abundant and had narrower substrate specificity, indicating that NMT expansion has contributed substantially to BIA chemodiversity in angiosperms, particularly in Ranunculales species. In summary, we not only characterized three novel enzymes that could be useful in the biosynthetic production of valuable BIAs but also shed light on the molecular origin of BIAs during angiosperm evolution.
Significance Statement
Benzylisoquinoline alkaloids (BIAs) are a class of plant secondary metabolites with great pharmacological value. Our study identified and functionally characterized a BIA N‐methyltransferase (LcNMT1) and two O‐methyltransferases (LcOMT1 and LcOMT3) in Liriodendron chinense, the first to be characterized from Magnoliid species. The magnoliales‐derived NMTs were less abundant and had narrower substrate specificity, suggesting that NMT expansion has contributed substantially to BIA chemodiversity in angiosperms, especially in Ranunculales species. |
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ISSN: | 0960-7412 1365-313X |
DOI: | 10.1111/tpj.15966 |