Carotenoid biosynthetic pathway
A chromoplast-specific carotenoid biosynthesis pathway is revealed by cloning of the tomato white-flower locus.
Carotenoid biosynthesis during tomato fruit ..
For those interested in scientific details about carotenoids, here's a scientific review that covers the mechanisms controlling (1) the first committed step in phytoene biosynthesis, (2) flux through the branch to synthesis of a- and b-carotenes and (3) metabolic feedback signalling within and between the carotenoid, MEP and ABA pathways; by Christopher Cazzonelli, published in the journal Functional Plant Biology in 2011 (with permission from CSIRO Publishing)
The first generation of Golden Rice showed that it was possible to produce provitamin A in rice grains, but it was recognised that to combat vitamin A deficiency more higher β-carotene levels would be required. As only two biosynthetic transgenes are required in the process, the logical approach was to identify the bottleneck of the biosynthetic pathway and fine-tune the enzymatic activities of the two gene products involved, phytoene-synthase (PSY) and carotene-desaturase (CRTI).
during carotenoid biosynthesis in tomato ..
Putative homologs of tomato components of the light signal transduction pathway, such as DE-ETIOLATED1 (DET1; originally identified as HIGH PIGMENT [hp2]), UV-DAMAGED DNA BINDING PROTEIN1 (DDB1; originally hp1) and CULLIN-4 (CUL4) were identified in watermelon (sequences Cla021340, Cla019536 and Cla019583, respectively – Table ). All three genes were expressed at a low level during watermelon fruit ripening with no significant variation (FDR > 0.05) suggesting they are probably not rate limiting in isoprenoid biosynthesis and associated fruit pigmentation.
ACAT2 catalyses the condensation of two acetyl-CoA subunits to form acetoacetyl-CoA thus directing this central metabolite to the MVA pathway. Interestingly ACAT2 mRNA expression was up-regulated approximately three-fold during watermelon ripening suggesting that this enzyme may divert the metabolic flux of acetyl-CoA from the biosynthesis of fatty acids and amino acids toward the synthesis of isoprenoids. 3-Hydroxy-3-methylglutaryl-CoA reductase (HMGR) is a key regulatory enzyme in the pathway and catalyses the formation of MVA from 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA). It is a highly regulated enzyme, being subjected to transcriptional, translational, and post-translational control . Although a sequence (Cla015723) coding for a putative HMGR1 is differentially expressed in ripening watermelon fruits (FDR = 0.0137) (Additional file : Table S1), it was not taken into account in this study having RPKM far below our defined minimal value of 8. However, the very low expression of hmgr 1 (0–0.3 RPKM) in ripening watermelon fruits supports the assertion that the conversion of HMG-CoA to MVA is the rate limiting step in the biosynthesis of sterols and other isoprenoids .
of carotenoid biosynthesis pathway ..
Taken together, these results suggest maintenance of many regulators in the watermelon genome in common with tomato, yet suggest a complex and, for many aspects, different regulatory system for isoprenoid biosynthesis between these fruits. While a common set of metabolic and regulatory genes influences carotenoid accumulation during development and ripening, specific regulatory systems may also differ possibly related to the different ripening physiologies of climacteric and non-climacteric fruits. As such, these data represent the starting point for characterizing conserved and distinct regulatory functions of isoprenoid biosynthesis in climacteric and non-climacteric species. They also provide information and targets for plant researchers and breeders to test as potential tools for watermelon crop improvement. Since this study was done only at the transcriptional level, subsequent experimentation is required to see if other changes arise at other levels of cellular regulation.
It requires 7 rounds of this pathway to degrade palmitate (a C16 fatty acid).
A graphic chart of these important metabolic steps may be found in the web site.
Regulation of carotenoid biosynthesis during tomato …
The carotenoid biosynthesis pathway in tomato
Analysis in vitro of the enzyme CRTISO establishes a poly-cis-carotenoid biosynthesis pathway in plants.
constitute the pathway of carotenoid biosynthesis in plants was ..
A chromoplast-specific carotenoid biosynthesis pathway is revealed by cloning of the tomato whiteflower locus.
A Chromoplast-Specific Carotenoid Biosynthesis Pathway …
Tomato (Solanum lycopersicum L.) is one of the model plant to study carotenoid biosynthesis
Beta Carotene | Biosynthesis | Metabolic Pathway
The absolute configuration of ceriporic acids, their stereoselective biosynthetic pathway and the diversity of their metabolites have been largely discussed ().
Boronat A: Carotenoid biosynthesis during tomato ..
Regulation 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.
carotenoid biosynthesis pathway is revealed ..
Rice produces β-carotene in the leaves but not in the grain, where the biosynthetic pathway is turned off during plant development. In two genes have been inserted into the rice genome by genetic engineering, to restart the carotenoid biosynthetic pathway leading to the production and accumulation of β-carotene in the grains. Both genes are naturally involved in carotene biosynthesis. The difference here is that the reconstructed pathway is not subject to downregulation, as usually happens in the grain.
To understand the response of carotenoid biosynthetic pathway to ..
To maximize the health-promoting benefits of carotenoids through increased consumption, characterization of carotenoid synthesis and accumulation in important food crops such as watermelon is essential. Understanding the molecular and genetic components controlling the carotenoid biosynthetic pathway is fundamental for targeted breeding aimed at improving carotenoid-producing watermelon cultivars [, ].
How the carotenoid biosynthetic pathway is regulated and what ..
Transformation of CrtR-b2 to tobacco improved the seed germination under salt stress condition, indicating that the hydrolysis of β-carotenoid is the target of transcriptional regulation of the carotenoid biosynthesis in both tomato cultivar and wild relative.
Molecular genetics of carotenoid biosynthesis pathway ..
In addition, CrtR-b1 and CrtR-b2 that encode β-carotenoid hydroxylases were the only genes in carotenoid biosynthetic pathway that were up-regulated by salt stress in both species.
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