Capsaicinoids biosynthesis

Blum, E., Mazourek, M., O Connell, M., Curry, J., Thorup, T., Liu, K., Jahn, M. and Paran, I. (2004) Molecular mapping of capsaicinoid biosynthesis genes and quantitative trait loci analysis for capsaicinoid content in Capsicum. Theoritical and Applied Genetics 108(1), 79-86. 

Aza-Gonzalez, C., H. G. Nimez-Palenius, and N. Ochoa-Alejo, Molecular biology of capsaicinoid biosynthesis in chili pepper (Capsicum spp.). Plant Cell. Rep., 2011. 30(5) p. 695-706. 

Capsaicinoids are synthesized by the condensation of vanillylamine with a short chain branched fatty acyl CoA. A schematic of this pathway is presented in Fig. 8.4. Evidence to support this pathway includes radiotracer studies, determination of enzyme activities, and the abundance of intermediates as a function of fruit development [51, 52, 57-63], Differential expression approaches have been used to isolate cDNA forms of biosynthetic genes [64-66], As this approach worked to corroborate several steps on the pathway, Mazourek et al. [67] used Arabidopsis sequences to design primers to clone the missing steps from a cDNA library. They have expanded the schema to include the biosynthesis of the key precursors phenylalanine and leucine, valine and isoleucine. Prior to this study it was not clear how the vanillin was produced, and thus the identification of candidate transcripts on the lignin pathway for the conversion of coumarate to feruloyl-CoA and the subsequent conversion to vanillin provide key tools to further test this proposed pathway. 

Validation of the role of femloyl-CoA in the synthesis of the vanillin precursor will be detection of the appropriate intermediates and/or enzyme activities in placental extracts that could account for the production of the predicted levels of capsaicinoids. The presence of low levels of monolignol intermediates could be explained by lignin biosynthesis. An alternate route from phenylalanine to vanillin has been considered by some investigators Orlova et al. [68] demonstrated the role of the benzenoid pathway in petunia flowers for the biosynthesis of phenylpropanoid/benzenoid volatiles. 

Blum E, Mazourek M, O Connell MA, Curry J, Thorup T, Liu K, Jahn MM, Paran I (2003) Molecular mapping of capsaiciniod biosynthesis genes and QTL analysis for capsaicinoid content in Capsicum. Theor Appl Genet 108 79-86... 

Studies carried out by Kopp and Jurenitsch (1981) on the biosynthesis of cap-saicinoids in C. annuum var. annuum established that valine, isoleucine and leucine were direct precursors of the respective even- and odd-numbered branched fatty acid moieties of the capsaicinoids. 

Yu et al. (2005) evaluated capsaicin biosynthesis in water-stressed hot pepper fruits. The concentration of capsaicin in the placenta of fruits in the water deficit treatment began to increase rapidly 10 DAF. It reached maximum at 30 DAF and was 3.84-fold higher than in the placenta of control treatment plants. In the pericarp, the concentration of capsaicin reached maximum at 50 DAF and was 4.52-fold higher than in the control treatment. PAL activity was higher in the placenta of fruits in the water deficit treatment than in the fruits of control plants at 50 DAF. At 40 or 50 DAF, cinnamic acid 4-hydroxylase (trans-cinnamate-4-monoox-ygenase) (C4H) activity was higher in plants subjected to the water deficit treatment than in control plants. Capsaicinoid synthase (CS) activity 40 DAF was 1.45- to 1.58-fold higher in fruits in the water deficit treatment than in fruits in the control treatment. 

Kopp, B. and Jurenitsch, J. (1981) Biosynthesis of capsaicinoids in Capsicum annuum var. annuum. II. Formation of the fatty acid moiety of the capsaicinoids from L-valine, L-leucine and L-isoleucine. Planta-Medica 43(3), 272-279. 

From a biogenetic standpoint, capsaicin is an acylated degraded phenylpropanoid. Both its aromatic and its acyl moiety are the result of unique metabolic processes that, though simple in principle, are still poorly characterized in terms of enzymology and regulation. Since vanillamine (23) is abundant in placental tissues of Capsicum, the only site of biosynthesis of capsaicinoids, the limiting factor for the synthesis of... 

Fig. 6.5 Biosynthesis of bianched-chain capsaicinoids starting with a branched amino acid, e.g., L-valine — 2-oxovalerate —> isobutyryl CoA —> elongation (-t 3 x malonyl CoA) —> [- 3 x COj] — (activated) 8-methylnonanoicacid+vanillylamine—>dihydiocapsaicin[R=(Cllj) CH(CH3)CHj] CS = capsaicin(oid) synthase...

In certain fruits the disappearance of phenolic acids may occur in relation to the biosynthesis of other phenolic compounds, for example, the decrease in hydroxycinnamic conjugates during growth and maturation of Vitis vinifera berries and the rapid increase in anthocyanin levels that occurs at the same time in the red cultivars [2]. In fruits of chili pepper (Capsicum frutescens) the onset of capsaicinoid accumulation and ligninlike material parallels the disappear-... 

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