Carotenoid pathway

The carotenoid pathway may also be regulated by feedback inhibition from the end products. Inhibition of lycopene cyclisation in leaves of tomato causes increase in the expression of Pds and Psy-1 (Giuliano et al, 1993 Corona et al, 1996). This hypothesis is supported by other studies using carotenoid biosynthesis inhibitors where treated photosynthetic tissues accumulated higher concentrations of carotenoids than untreated tissues (reviewed by Bramley, 1993). The mechanism of this regulation is unknown. A contrary view, however, comes from studies on the phytoene-accumulating immutans mutant of Arabidopsis, where there is no feedback inhibition of phytoene desaturase gene expression (Wetzel and Rodermel, 1998). 

Unicelluar algal and bacterial genes were the first to be isolated and characterized and led to the isolation of most of the higher plant genes involved in carotenoid biosynthesis. Carotenogenic gene clusters from bacteria and algae" - - - contributed immensely to the elucidation of the carotenoid pathway. 

FIGURE 5.3.5 Enhancement of lycopene accumulation in . coZi by over-expression of DXS. Lycopene accumulation (left) is enhanced (right) when E. coli cells carrying a carotenoid pathway gene cassette (+EIB) are further transformed with a dxs gene on a multicopy plasmid (+E1B +dxs). Lycopene hyperaccumulation was demonstrated by Matthews and Wurtzel. ... 

Understanding mechanisms controlling metabolon localization in plastids of different membrane architectures Little is known about metabolon structure, assembly, and membrane targeting. The carotenoid biosynthetic pathway exists on plastid membranes. However, plastids have different membrane architectures and therefore tissue- and plastid-specific differences in membrane targeting of the biosynthetic metabolon can be expected. Localization in chloroplasts that harbor both thylakoid and envelope membranes differs from the envelope membranes in endosperm amy-loplasts. In fact, localization on both thylakoid and envelope membranes implies that the carotenoid pathway is really not a single pathway, but a duplicated pathway that may very well have membrane-specific roles with regard to functions in primary and secondary metabolism. 

Analysis in diverse lines can facilitate identification of useful alleles that control expression of enzymes upstream of the carotenoid pathway, a feature that would not be evident from conventional end-product screening of breeding lines. Moreover, this characterization sets the stage for marker-assisted selection of superior endogenous alleles and facilitates selection of introduced transgenes that may be necessary to supplement the genotypic contribution required for a particular plant chemical outcome. 

Matusova, R. et ah, The strigolactone germination stimulants of the plant-parasitic Striga and Orobanche spp. are derived from the carotenoid pathway, Plant Physiol. 139, 920, 2005. 

SmoUce, C.D., Martin, V.J.J., and Keasling, J.D., Controlling the metabolic flux through the carotenoid pathway using directed mRNA processing and stabilization, Metabol. Eng. 3, 313, 2001. 

Prado-Cabrero, A., A. F. Estrada et al. (2007). Identification and biochemical characterization of a novel carotenoid oxygenase Elucidation of the cleavage step in the Fusarium carotenoid pathway. Mol. Microbiol. 64(2) 448 160. 

Saelices, L., L. Youssar et al. (2007). Identification of the gene responsible for torulene cleavage in the Neurospora carotenoid pathway. Mol. Gen. Genomics 278(5) 527-537. 

Inlet Figure Cell pellets with carotenoid pathway products (Schmidt-Dannert, 2000). JM 109 transformants expressing wild-type and mutant cyclases. 

At present, there is no doubt about the biosynthesis of ABA by the carotenoid pathway via the MEP pathway in plants. If ABA is biosynthesized by the direct pathway, the first cyclized intermediate will be ionylide-neethanol, having a hydroxyl group at C-l derived from farnesol however, ionylideneethanol has not been found in plants, so the direct pathway is not involved in ABA biosynthesis. The mevalonic acid pathway may also be excluded because almost no 13C label was incorporated into the carbons, which would be labeled in the mevalonic acid pathway in a feeding experiment with [l-13C]-D-glucose.640... 

Baumes, R., Wirth, J., Bureau, S., Giinata, Z., Razungles, A. (2002). Biogeneration of Ci3 noiisoprenoid compounds Experiments supportive for an apo-carotenoid pathway in grapevines. Anal. Chim. Acta, 458, 3-14. 

Very few published examples of the genetic manipulation of terpenoid biosynthesis are available, but two interesting successes have been achieved in the area of terpenoid vitamins for example, the ratio of beneficial tocopherol (vitamin E) isomers in oilseeds has been altered by this means and increased P-carotene (a vitamin A precursor) in both rice kernels and rapeseed has been obtained by manipulating the carotenoid pathway [361]. 

Phytoene desaturase and lycopene cyclase New carotenoid pathway (substrate and reaction specificity) Production of torulene in E.coli DNA family shuffling+ screening E. coli [209]... 

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

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