Carotenogenesis

Spirilloxanthin pathway (normal spirilloxanthin, unusual spirilloxanthin, spheroidene, and carotenal pathways). 

Okenone pathway (okenone, and. g.-keto carotenoid pathways). 

Most of the aerobic photosynthetic bacteria so far desaibed have the spirilloxanthin pathway, further some also have unusual carotenoids as described below. 

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Although carotenogenesis in plants takes place in plastids, all of the carotenoid biosynthesis genes are nuclear encoded and their polypeptide products are imported into the plastids. Therefore, they contain a N-terminal transit peptide sequence. For example, the size of the transit peptide of PSY from ripe tomato fruit is approximately 9 kDa, corresponding to about 80 amino acid residues (Misawa et al, 1994). 

Clearly, the control of gene expression at the transcriptional level is a key regulatory mechanism controlling carotenogenesis in vivo. However, post-transcriptional regulation of carotenoid biosynthesis enzymes has been found in chromoplasts of the daffodil. The enzymes phytoene synthase (PSY) and phytoene desaturase (PDS) are inactive in the soluble fraction of the plastid, but are active when membrane-bound (Al-Babili et al, 1996 Schledz et al, 1996). The presence of inactive proteins indicates that a post-translational regulation mechanism is present and is linked to the redox state of the membrane-bound electron acceptors. In addition, substrate specificity of the P- and e-lycopene cyclases may control the proportions of the p, P and P, e carotenoids in plants (Cunningham et al, 1996). 

A further consideration in the choice of gene relates to those that are members of a gene family. Only one member of such a family may be involved in carotenogenesis in a particular tissue. A good example of this is Psy-1 and-2 of tomato. PSY-1 is responsible for phytoene synthesis in ripening fruit (Fraser et al, 1999) whereas PSY-2 is not functional in chromoplasts, even if the protein is produced. 

We have chosen carotenoid biosynthesis as the example system for demonstrating the prospects of biotechnology of food colorants for several reasons. Carotenoid biosynthesis is the second most understood system. Multiple examples of valuable food colorant engineering in fungi, bacteria, and plants have been reported. Finally, carotenogenesis in cereal crops such as maize and rice is the primary focus of our research efforts. Hopefully, we provide the food technologist with a template with which to examine other industrially important pigment systems. 

In a very recent study in potatoes, inhibition of LCYE accumulation was accomplished by an antisense LcyE driven by the patatin promoter and allowed rechanneling of lycopene toward the P-carotene branch of the pathway to produce up to 14-fold increased levels of P-carotene as well as up to 2.5-fold increased total carotenoids. RNAi and TILLING for manipulation of carotenogenesis have yet to be reported, but these new techniques for suppression of function and generation and selection of allelic diversity are likely to impact future research and production of varieties with enhanced pigment accumulation. 

Careful empirical selection of the expression platform for carotenogenesis has included selection of the best strains for stability and degree of accumulation and the selection of compatible drug-resistance combinations and low copy number polycistronic plasmids to enhance product accumulation by decrease of metabolic burden." 5 Matthews and Wurtzel discussed culture and induction conditions - that have been explored in most studies. Most efforts to engineer carotenoid biosynthesis in E. coli focused on the genes and enzymes of the pathway and had a modest effect on improved accumulation. For example, substitution and over-expression of a GGPPS that uses IPP directly (discussed in... 

Plant use is less biotechnologically advanced and fundamentally more complex. The first generation of plant metabolic engineering met with mixed success and produced unanticipated results — problems that are not necessarily restricted to manipulation of carotenogenesis. The reason is that predictive metabolic engineering relies on the establishment of both needed tools and an information infrastructure... 

Matthews, P.D., Carotenogenesis in Maize and Rice, Graduate School and University Center, City University of New York, 2001. 

Masamoto, K. et al.. Identification of a gene required for cis-to-trans carotene isomerization in carotenogenesis of the cyanobacterium Synechocystis sp. PCC 6803, Plant Cell Physiol. 42, 1398, 2001. 

Fig. 14. Action spectra for light-induced metabolic responses. (1) oxygen uptake in Chlorella200, and carotenogenesis of (S) Neurospora44), (4) Mycobacterium91), (5) Fusarium14l Curve (2) shows the absorption spectrum of an extract of Mycobacterium possibly containing the bluelight photoreceptor112). Compare curve (2) to the action spectrum (4)...

The second step of carotenogenesis, the period of protein synthesis, has clearly been separated from the sensory transduction by means of the inhibitors of protein synthesis cycloheximide12 78 142) and chloramphenical12 146 147). Regardless of their presence, light-induction was feasible, but carotenogenesis took place only after their removal. 

Action spectrum for light-induced carotenogenesis in Neurospora44) ... 

Further genetic studies have provided additional information about the regulation of carotenogenesis in Phycomyces blakesleeanus. ... 

Morris, W. L., Duereux, L., Griffiths, D. W., Stewart, D., Davies, H. V., Taylor, M. A. (2004). Carotenogenesis during tuber development and storage in potato. Journal of Experimental Botany, 55, 975-982. 

T. Goodwin, Biocbem. J. 68, 503-511 (1958), Studies in Carotenogenesis 24. The Changes in Carotenoid and Chlorophyll Pigments in the Leaves of Deciduous Trees During Autumn Necrosis. ... 

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