A flavonol O-methyltransferase from Catharanthus roseus performing two sequential methylations

Area of Science:

• Plant Biochemistry
• Molecular Biology
• Enzyme Function

Background:

• Catharanthus roseus produces diverse indole alkaloids and flavonoids.
• O-methyltransferases (OMTs) are crucial enzymes in plant secondary metabolism.
• Previous studies focused on OMTs involved in indole alkaloid biosynthesis.

Purpose of the Study:

• To purify and characterize O-methyltransferase activities from Catharanthus roseus.
• To identify novel OMTs involved in plant secondary metabolite biosynthesis.
• To elucidate the function of newly identified OMTs, specifically CrOMT2 and CrOMT4.

Main Methods:

• Protein extraction and purification from cell suspension cultures.
• Affinity chromatography and SDS-PAGE for protein enrichment and analysis.
• Mass spectrometry and homology-based RT-PCR for protein identification and cDNA cloning.
• Recombinant protein expression in E. coli for functional enzyme assays.

Main Results:

• Enrichment of 16-hydroxytabersonine O-methyltransferase (16HT-OMT) activity revealed two dominant proteins (CrOMT2, CrOMT4).
• CrOMT4 showed no detectable activity; CrOMT2 was identified as a flavonoid OMT, not 16HT-OMT.
• CrOMT2 catalyzes sequential methylation of myricetin and dihydromyricetin, characteristic of C. roseus flavonol glycosides and anthocyanins.

Conclusions:

• CrOMT2 represents a novel OMT involved in flavonoid biosynthesis in Catharanthus roseus.
• The study re-evaluates the enzyme composition and metabolic pathways in C. roseus.
• CrOMT2's function is critical for the production of specific methylation patterns in plant pigments.