Mark Harker

Metabolic engineering of astaxanthin production in tobacco flowers

Using metabolic engineering, we have modified the carotenoid biosynthesis pathway in tobacco (Nicotiana tabacum) to produce astaxanthin, a red pigment of considerable economic value. To alter the carotenoid pathway in chromoplasts of higher plants, the cDNA of the gene CrtO from the alga Haematococcus pluvialis, encoding β-carotene ketolase, was transferred to tobacco under the regulation of the tomato Pds (phytoene desaturase) promoter. The transit peptide of PDS from tomato was used to target the CRTO polypeptide to the plastids. Chromoplasts in the nectary tissue of transgenic plants accumulated (3S,3′S) astaxanthin and other ketocarotenoids, changing the color of the nectary from yellow to red. This accomplishment demonstrates that plants can be used as a source of novel carotenoid pigments such as astaxanthin. The procedures described in this work can serve as a platform technology for future genetic manipulations of pigmentation of fruits and flowers of horticultural and floricultural importance.

Biosynthesis of ketocarotenoids in transgenic cyanobacteria expressing the algal gene for β-C-4-oxygenase, crtO

© 1997 Federation of European Biochemical Societies.

Molecular genetics of the carotenoid biosynthesis pathway in plants and algae

During recent years genes for more than 20 different carotenogenic enzymes have been cloned from various organisms: bacteria, cyanobacteria, fungi, algae and plants. This accomplishment has provided new molecular tools to study the enzymes and yielded new information on their structure, function and regulation. We describe here the recent progress in the molecular genetics of the carotenoid biosynthesis pathway in plants. To date, the genes for almost all the enzymes, from the early steps of the isoprenoid pathway to the predominant xanthophylls, have been cloned. Their characterization had an immense impact on our understanding of carotenoid biosynthesis at the molecular level.

Paracoccus marcusii sp. nov., an orange gram-negative coccus.

Phenotypic, chemotaxonomic and 16S rDNA sequence analysis of an orange Gram-negative coccus that appeared as a contaminant on a nutrient agar plate delineated a new species of the genus Paracoccus. Phenotypic features of the strain that differ from all or most of the previously described Paracoccus species include its bright orange colour, caused by the synthesis of large amounts of carotenoids (mainly astaxanthin), and its inability to use nitrate as an electron acceptor in respiration. The name Paracoccus marcusii is proposed for this organism. The type strain is DSM 11574T.

[17] Molecular biology of carotenoid biosynthesis in photosynthetic organisms

Publisher Summary Carotenoids serve two major functions in photosynthesis: as accessory pigments for light harvesting and in the prevention of photooxidative damage. Carotenoids also serve structural functions in the photosynthetic pigment- protein complexes of the reaction centers and the light-harvesting antennae, where they are bound to specific chlorophyll/carotenoid-binding proteins. They provide yellow, orange, or red coloring to many flowers, fruits, mushrooms, and animals. Carotenoid biosynthesis genes in plants, algae, and cyanobacteria are generally not conserved with those of bacteria and, therefore, the latter could not serve as molecular probes for cloning the plant-type genes. In addition, the genes in eukaryotes are dispersed throughout the genome. In cyanobacteria, only two genes, for phytoene desaturase and phytoene synthase, are in the same operon, while all other genes are dispersed. All carotenoids are related biosynthetically and share a common early pathway with other isoprenoids. These reactions, in which mevalonate is an important intermediate, yield the monomer building block for all products in the isoprenoid pathway, the C 5 molecule isopentyl diphosphate.