The evolution of strictly monofunctional naphthoquinol C-methyltransferases is vital in cyanobacteria and plastids

Lauren Stutts, Scott Latimer, Zhaniya Batyrshina, Gabriella Dickinson, Hans Alborn, Anna K. Block, Gilles J. Basset

Research output: Contribution to journalArticlepeer-review


Prenylated quinones are membrane-associated metabolites that serve as vital electron carriers for respiration and photosynthesis. The UbiE (EC (EC C-methyltransferases catalyze pivotal ring methylations in the biosynthetic pathways of many of these quinones. In a puzzling evolutionary pattern, prokaryotic and eukaryotic UbiE/MenG homologs segregate into 2 clades. Clade 1 members occur universally in prokaryotes and eukaryotes, excluding cyanobacteria, and include mitochondrial COQ5 enzymes required for ubiquinone biosynthesis; Clade 2 members are specific to cyanobacteria and plastids. Functional complementation of an Escherichia coli ubiE/menG mutant indicated that Clade 1 members display activity with both demethylbenzoquinols and demethylnaphthoquinols, independently of the quinone profile of their original taxa, while Clade 2 members have evolved strict substrate specificity for demethylnaphthoquinols. Expression of the gene-encoding bifunctional Arabidopsis (Arabidopsis thaliana) COQ5 in the cyanobacterium Synechocystis or its retargeting to Arabidopsis plastids resulted in synthesis of a methylated variant of plastoquinone-9 that does not occur in nature. Accumulation of methylplastoquinone-9 was acutely cytotoxic, leading to the emergence of suppressor mutations in Synechocystis and seedling lethality in Arabidopsis. These data demonstrate that in cyanobacteria and plastids, co-occurrence of phylloquinone and plastoquinone-9 has driven the evolution of monofunctional demethylnaphthoquinol methyltransferases and explains why plants cannot capture the intrinsic bifunctionality of UbiE/MenG to simultaneously synthesize their respiratory and photosynthetic quinones.

Original languageEnglish
Pages (from-to)3686-3696
Number of pages11
JournalPlant Cell
Issue number10
StatePublished - 1 Oct 2023
Externally publishedYes

ASJC Scopus subject areas

  • Plant Science


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