Carotenoid Biosynthesis in Higher Plants

Carotenoids of higher plants, algae, and fungi are C40 tetraterpenes biosynthesized by the well-known isoprenoid pathway [1, 5, 6, 8, 17, 18]. The early steps, involving the formation of the C5 isoprenoid units and the subsequent synthesis of prenyldiphosphate intermediates, are common to all classes of terpenoids. 

The first specific precursor for terpenoids in the cytoplasma is the Cg molecule mevalonic acid (MVA), which is built via the classical acetate/mevalonate pathway and converted by a series of phosphorylating and decarboxylation reactions into C5 isopentenyldiphosphate (IPP), the universal building block for chain elongation up to C20. In the chloroplasts, the biosynthesis of IPP starts from glyceraldehyde-3-phosphate and pyruvate to give l-deoxy-D-xylulose-5-phosphate (DOXP) via the non-mevalonate pathway as a recently detected alternative IPP route [19]. The reaction is catalyzed by the enzyme DOXP synthase and can be inhibited by a breakdown product of the herbicide clomazone [12]. 

After 1,3-allylic isomerization of IPP to dimethylallyl pyrophosphate (DMAPP) by the enzyme IPP isomerase, another IPP unit is added to yield Cio geranylpyro-phosphate (GPP). 

Subsequent addition of a second or third molecule of IPP leads to the formation of Ci5 farnesyl pyrophosphate (FPP) and the C20 geranylgeranyl pyrophosphate (GGPP). The chain elongation is a head-to-tail condensation process, which forms carbon-carbon bonds between C-4 of IPP and C-1 of the aDyhc 

DMAPP dimethylallyl pyrophosphate FPP farnesyl pyrophosphate GPP geranyl pyrophosphate  

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Britton, G. (1982). Carotenoid biosynthesis in higher plants. Physiol Veg., 20, 735-755. 

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