A Polyphenol Oxidase Catalyzes Aurone Synthesis in Marchantia polymorpha

Area of Science:

• Plant Biochemistry
• Evolutionary Biology
• Molecular Botany

Background:

• Aurones are key flavonoid compounds with a distinct furanone structure.
• Higher plants exhibit convergent evolution in aurone biosynthesis pathways.
• Aurone biosynthesis in bryophytes, including pathways and enzymes, remains largely uncharacterized.

Purpose of the Study:

• To identify and characterize enzymes responsible for aureusidin biosynthesis in the model liverwort Marchantia polymorpha.
• To investigate the evolutionary origins of aureusidin synthase enzymes in land plants.

Main Methods:

• Enzyme assays using Marchantia polymorpha extracts and recombinant proteins.
• Overexpression of specific genes (MpMYB14) in M. polymorpha to study metabolite accumulation.
• Biochemical characterization of identified enzymes, including substrate specificity and inhibitor sensitivity.
• Heterologous expression of candidate enzymes in Saccharomyces cerevisiae.

Main Results:

• Identification of a polyphenol oxidase, MpAS1, as aureusidin synthase in M. polymorpha.
• MpAS1 catalyzes aureusidin biosynthesis from naringenin chalcone and converts it to riccionidin A.
• MpAS1 exhibits substrate promiscuity, with highest activity on eriodictyol chalcone.
• The identified PPO family in M. polymorpha shows independent evolution from those in higher plants.

Conclusions:

• Aureusidin biosynthesis in Marchantia polymorpha is mediated by MpAS1, a member of the polyphenol oxidase family.
• Aureusidin synthases have evolved independently and in parallel across different land plant lineages.
• This study provides insights into the convergent evolution of secondary metabolite pathways in plants.