Coenzyme Q10 Biosynthesis in Plants: Is the Polyprenyltransferase an Appropriate Gene Target for the Increased Production of CoQ

Coenzyme Q10, CoQ10, is a valuable compound found in all organisms that perform oxidative phosphorylation. Its function and biosynthesis have been well studied in model systems such as E. coli and yeast; however, these are less well understood in plants where CoQ10 participates in a number of other cellular functions such as 'alternative' electron transport associated with the plant response to oxidative stress. CoQ10 biosynthesis in plants shares many similarities with other systems based on gene homology and accumulated biosynthetic intermediates. Understanding CoQ10 biosynthesis and its metabolic engineering in plants is increasingly important due to its use in treating heart and other diseases and its use as an antioxidant in both cosmetics and nutraceuticals. This work reviews the various known and postulated biological functions, the biosynthesis, and the metabolic engineering of CoQ 10 in plants. A reliable HPLC-UV method for the routine quantification of CoQ10 in tobacco leaves which allowed for the description of the occurrence of CoQ10 within a leaf, at different stalk positions of the tobacco plant, and through time in a greenhouse is described. Further, haploid genotypes of burley and flue-cured tobaccos, TN90LC and NC55, respectively, were transformed via Agrobacterium-mediated transformation with the gene encoding the Arabidopsis thaliana 4-hydroxybenzoate polyprenyl diphosphate transferase. Individual T0 transgenic plants were identified as having increased CoQ10 content. A transgenic line from self-fertilized, doubled haploid progeny was identified from each NC55 and TN90LC with increased CoQ10 content, 60% and a 40%, respectively, due to a statistically significant genotype effect. Transgenic lines with improved CoQ10 showed an apparent ability to recover from increasing NaCl stress better than non-transgenics. The transgenics recovered equally as well as non-transgenic tissue culture-derived tobaccos also identified as having increased CoQ10. The transgenic DH1 NC55 line with increased CoQ10 displayed no difference in an isoprenoid profile when monitoring chloroplast-derived isoprenoids by LC-APCI-MS/MS.