Carotenoid biosynthesis is up-regulated by strong light in the cyanobacterium Synechococcus . By blocking off the pathway at the level of phytoene conversion, lightdependent accumulation of phytoene was observed. Realtime PCR studies demonstrated that four genes of the carotenogenic pathway are under transcriptional control. These were the genes encoding phytoene synthase, phytoene desaturase, z -carotene desaturase and b -carotene hydroxylase. The transcript of the first three follow a similar kinetics, whereas the transcript of b -carotene hydroxylase increased much faster upon transfer to high light. Promoter activities were determined with transcriptional fusions to chloramphenicol acyltransferase as reporter enzyme. The activity of the promoter of the phytoene desaturase/synthase operon was higher under strong light.

Sansalvamide is a cyclic pentadepsipeptide produced by Fusarium solani and has shown promising results as potential anti-cancer drug. The biosynthetic pathway has until now remained unidentified, but here we used an Agrobacterium tumefaciens-mediated transformation (ATMT) approach to generate knockout mutants of two candidate non-ribosomal peptide synthetases (NRPS29 and NRPS30). Comparative studies of secondary metabolites in the two deletion mutants and wild type confirmed the absence of sansalvamide in the NRPS30 deletion mutant, implicating this synthetase in the biosynthetic pathway for sansalvamide. Sansalvamide is structurally related to the cyclic hexadepsipeptide destruxin, which both contain an α-hydroxyisocaproic acid (HICA) unit. A gene cluster responsible for destruxin production has previously been identified in Metarhizium robertsii together with a hypothetical biosynthetic pathway. Using comparative bioinformatic analyses of the catalytic domains in the destruxin and sansalvamide NRPSs, we were able to propose a model for sansalvamide biosynthesis. Orthologues of the gene clusters were also identified in species from several other genera including Acremonium chrysogenum and Trichoderma virens, which suggests that the ability to produce compounds related to destruxin and sansalvamide is widespread.

Ketocarotenoids and especially astaxanthin are high‐valued pigments used as feed additives. Conventionally, they are provided by chemical synthesis. Their biological production is a promising alternative. For the development of a plant production system, Nicotiana glauca, a species with carotenoid‐containing yellow pigmented flower petals, was transformed with a cyanobacterial ketolase gene. The resulting plants accumulated 4‐ketozeaxantin (adinoxanthin), which is the first ketocarotenoid synthesized in flower petals by genetic modification. Due to the very late flowering in this tobacco species, N. tabacum was used to optimize the yield and ketocarotenoid product pattern by metabolic engineering of the ketolation steps of carotenogenesis. The highly carotenogenic nectary tissue in the flowers represents a model of a flower chromoplast system. By expression of a ketolase gene, it was possible to engineer the biosynthetic pathway towards the formation of 3'‐hydroxyechinenone, 3‐hydroxyechinenone, 4‐ketozeaxanthin, 4‐ketozeaxanthin esters, 4‐ketolutein and 4‐ketolutein esters. Some of these ketocarotenoids were also formed in the leaves of the trangenic plants. In particular, by co‐expression of the ketolase gene in combination with a hydroxylase gene under an ubiquitous promoter, the formation of total carotenoids in nectaries increased by more than 2.5‐fold. In the nectaries of this type of transformants, more than 50% of the accumulating carotenoids were keto derivatives. In addition, the levels of ketocarotenoid esters were much lower and a higher percentage of the free ketocarotenoids accumulated. These results open new promising perspectives for a successful metabolic engineering of keto‐hydroxy carotenoid production in carotenogenic flowers.

In purple bacteria, acyclic 1-methoxy carotenoids like spheroidene or spirilloxanthin are essential components of the photosynthetic apparatus. One of the last steps of their biosynthesis involves O-methylation of the 1-hydroxy group. The 1-HO-carotenoid methylase CrtF from Rhodobacter capsulatus catalyzing this type of reaction was expressed in Escherichia coli in an active form. It was then purified by affinity chromatography and biochemically characterized. The enzymatic reaction depends on S-adenosylmethionine as the only cofactor. By complementation in E. coli, the substrate specificity of the enzyme was determined. It could be shown that the enzyme converts not only all possible 1-hydroxy carotenoids in the spheroidene/1P-HO-spheroidene biosynthetic pathway of R. capsulatus but also carotenoid intermediates leading to the formation of spirilloxanthin in a pathway which is absent in R. capsulatus but present in related species.