Biochemistry

Abstract

CS-11-1 - Genetic and Biochemical Dissection of an Unsuspected Route for the Biosynthesis of Plant Coenzyme Q

Monday, July 16
1:03 PM - 1:23 PM

Coenzyme Q (ubiquinone) is a prenylated benzoquinone that serves as a vital electron carrier in the respiratory chain of mitochondria and some bacteria. In plants, approximately half of coenzyme Q's pool comes from the β-oxidative metabolism of phenylpropanoids in peroxisomes; the metabolic origin of the other half is still unknown. Using transcriptional network modeling in Arabidopsis, we have identified a functional connection between the metabolism of coenzyme Q and that of flavonoids in the cytosol. Targeted metabolite profiling in a series of Arabidopsis mutants corresponding to the central flavonoid biosynthetic pathway showed that loss of function of flavanone-3-hydroxylase and upstream enzymes, resulted in a marked decrease in coenzyme Q content. By contrast, mutations of the enzymes located downstream of the flavanone-3-hydroxylase catalyzed reaction had no effect on coenzyme Q level. The tomato mutant anthocyanin reduced displayed a similar loss of coenzyme Q in leaves. Conversely, tomato fruits engineered to accumulate flavonoids contained significantly more coenzyme Q than their wild-type counterparts. These data not only confirm that the biosynthesis of coenzyme Q is connected to that of flavonoids, but also pinpoint kaempferol as a branch-point metabolite between these pathways. Agreeing with such a scenario, the exogenous supply of kaempferol to flavanone-3-hydroxylase knockout plants rescued coenzyme Q content to wild-type level, while naringenin did not. Feeding experiments using phenylalanine-[Ring 13C6] coupled to liquid chromatography-tandem mass spectrometry analysis demonstrated that phenyl ring B of flavonoids is incorporated into coenzyme Q via the formation of 4-hydroxybenzoate. Furthermore, enzymatic assays using kaempferol as substrates showed that peroxidase activities are responsible for the cleavage of the phenyl ring of these compounds, generating 4-hydroxybenzoate. All together, these results establish the existence of an alternative pathway for the biosynthesis of the benzenoid precursor of plant coenzyme Q, branching from that of flavonoids.


 

Co-Authors

Timothy Johnson – University of Florida, Gainesville, FL 32611; Anna Block – Agricultural and Veterinary Entomology, ARS, USDA, Gainesville, Florida, 32608; Scott Latimer – University of Florida, Gainesville, Florida 32611; Jeong Im Kim – University of Florida, Gainesville, Florida 32611; Eugenio Butelli – John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK; Clint Chapple – Purdue University, West Lafayette, IN 47907; Thomas Colquhoun – University of Florida, Gainesville, FL 32611; Cathie Martin – John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK; Gilles Basset – University of Florida, Gainesville, Florida 32611

Eric Soubeyrand

Postdoctoral research
University of Florida

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