Tomatoes carotenoid biosynthesis

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). 

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). 

BIRD C R, RAY J A, FLETCHER J D, BONIWELL J M, BIRD A S, TEULIERES C, BLAIN I, BRAMLEY P M and SCHUCH w (1991) Using antisense RNA to study gene function inhibition of carotenoid biosynthesis in transgenic tomatoes , BioTechnology, 9, 635-9. 

BRAMLEY p M (1997) The regulation and genetic manipulation of carotenoid biosynthesis in tomato fruit , PureAppl Chem, 69, 2159-62. 

FRASER P D, TRUESDALE M R, BIRD C R, SCHUCH W and BRAMLEY P M (1994) CarOtenoid biosynthesis during tomato fruit development . Plant Physiol, 105, 405-13. 

GiuLiANO G, BARTLEY G E and scoLNiK p A (1993) Regulation of carotenoid biosynthesis during tomato fruit development . Plant Cell, 5, 379-87. 

RONEN G, COHEN M, ZAMIR D and HIRSCHBERG J (1999) Regnlation of carotenoid biosynthesis during tomato fruit development expression of the gene for lycopene epsilon cyclase is down regulated during ripening and is elevated in the mutant delta . Plant J, 17, 341-51. 

TRUESDALE M R (1994) Carotenoid biosynthesis in the tomato, PhD thesis. University of London. 

Lois, L.M. et al.. Carotenoid biosynthesis during tomato fruit development regulatory role of 1-deoxy-D-xylulose 5-phosphate synthase. Plant J. 22, 503, 2000. 

Bartley, G.E. et ah, A tomato gene expressed during fruit ripening encodes an enzyme of the carotenoid biosynthesis pathway, J. Biol. Chem. 267, 5036, 1992. 

Enzyme Systems. Carotenoid biosynthesis by crude cell-free preparations from Halobacterium cutirubrum 0-carotene), Phycomyces blakesleeanus mutants (/8-carotene), and a Neurospora crassa mutant (phytoene) has been demonstrated. Detailed studies of carotenogenic enzymes from tomato fruit... 

Carotenoids are the major source of pro-vitamin A in our diet. Fortunately, they are relatively heat stable and do not suffer extensive loss during thermal processing. However, most carotenoids are sensitive to photoxidation and may lose their bright color under long exposure to light and oxygen. In intact fresh tomatoes, light can promote carotenoid biosynthesis (8). 

Gabellini N, Bowyer JR, Hurt E, Melandri A and Hauska G (1982) A cytochrome b/c complex with ubiquinol-cytochrome C2 oxidoreductase activity from Rhodopseudo-monas sphaeroides. Eur J Biochem 126 105-111 Gilmore AM (1996) Mechanistic aspects of xanthophyll cycle-dependent photoprotection in higher plant chloroplasts and leaves. Physiol Plantarum 98 1-13 Giuliano G, Bartley GE and Scolnik PA (1993) Regulation of carotenoid biosynthesis during tomato development. Plant Cell 5 379-387... 

GIULIANO, G., BARTLEY, G. E., SCOLNIK, P. A., Regulation of carotenoid biosynthesis during tomato development. Plant Cell 1993,5, 379-387. 

Apel, W., and Bock, R. (2009) Enhancement of carotenoid biosynthesis in transplastomic tomatoes by induced lycopene-to-provitamin A conversion. Plant Physiol, 151, 59-66. 

Temperature effects on carotenoid biosynthesis have been observed with F. aquaeductuum and N. crassa. Quantitative effects are observed in Phy-comyces and the yeasts Rhodotorula rubra and R. penaus. Qualitative changes have been observed in Rhodotorula glutinis. In ripening tomatoes, the synthesis of lycopene, but not /3-carotene, is inhibited in firuit held above 30°C (Goodwin and Jamikom, 1952 Tomes et al., 1956 Czygan and Wil-luhn, 1%7). However, the amount of /3-carotene formed in these fruits is relatively small. 

Wurbs D, Ruf S, Bock R (2007) Contained metabolic caigineering in tomatoes by expression of carotenoid biosynthesis genes from the plastid genrane. Plant J 49 276-288... 

In tomato two PSY encoding genes have been identified Psy-1 and Psy-2. Psy-1 encodes the fruit-ripening-specific isoform, which has been proved to be the key enzyme in the control of carotenoid biosynthesis [28]. Psy-2 encoded enzyme predominates in green tissues (including mature green fruit) and petals and has no role in carotenoid synthesis in ripening fruit [29, 26]. As an example of the role of this enzyme in carotenoid biosynthesis, a null mutation in Psy-1 in the yellow-flesh (r) mutant arrests carotenoid synthesis [30]. In this mutant, the accumulation of the flavonoid rutin in the fruit skin would lead to the development of yellowish fruits. 

Scheme 92.1 Carotenoid biosynthesis pathway in tomato (Adapted from [18], [25], [26] and [27]). Mutants for each enzyme are identified in square brackets. Genes involved in external regulation represented in the squares...

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