Plant phenylpropanoid pathway

First, Ro and Douglas constructed the initial steps of the plant phenylpropanoid pathway by connecting two enzymes, PAL and C4H, with a cytochrome P450 reductase (CPR) from a plant source in S. cerevisiae [31]. This heterologous transfer of plant phenylpropanoid pathway genes into yeast became the platform for the biosynthesis of various flavonoids and related compounds in microbial... 

Wuyts N, Swennen R, De Waele D (2006) Effects of plant phenylpropanoid pathway products... 

TEUTSCH, H.G., HASENFRATZ, M.P., LESOT, A., STOLTZ, C., GARNIER, J.M., JELTSCH, J.M., DURST, F., WERCK-REICHHART, D., Isolation and sequence of a cDNA encoding the Jerusalem artichoke cinnamate 4-hydroxylase, a major plant cytochrome P450 involved in the general phenylpropanoid pathway, Proc. Natl. Acad. Sci. USA, 1993,90,4102-4106. 

Dixon RA, Achnine L, Kota P, Liu CJ, Reddy MSS, Wang LJ (2002) The phenylpropanoid pathway and plant defence - a genomics perspective. Mol Plant Pathol 3 371-390 Dixon RA, Paiva NL (1995) Stress-induced phenylpropanoid metabolism. Plant Cell 7 1085-1097... 

Schalk, M., Cabello-Hurtado, F., Pierrel, M.A., Atanossova, R., Saindrenan, P. and Werck-Reichhart, D. (1998) Piperonylic acid, a selective, mechanism-based inactivator of the trans-annarrate 4-hydroxylase a new tool to control the flux of metabolites in the phenylpropanoid pathway. Plant Physiology, 118 (1), 209-218. 

The 4-coumarate CoA ligase (4CL EC 6.2.1.12) enzyme activates 4-coumaric acid, caffeic acid, ferrulic acid, and (in some cases) sinapic acid by the formation of CoA esters that serve as branch-point metabolites between the phenylpropanoid pathway and the synthesis of secondary metabolites [46, 47]. The reaction has an absolute requirement for Mg " and ATP as cofactors. Multiple isozymes are present in all plants where it has been studied, some of which have variable substrate specificities consistent with a potential role in controlling accumulation of secondary metabolite end-products. Examination of a navel orange EST database (CitEST) for flavonoid biosynthetic genes resulted in the identification of 10 tentative consensus sequences that potentially represent a multi-enzyme family [29]. Eurther biochemical characterization will be necessary to establish whether these genes have 4CL activity and, if so, whether preferential substrate usage is observed. 

The tightly regulated pathway specifying aromatic amino acid biosynthesis within the plastid compartment implies maintenance of an amino acid pool to mediate regulation. Thus, we have concluded that loss to the cytoplasm of aromatic amino acids synthesized in the chloroplast compartment is unlikely (13). Yet a source of aromatic amino acids is needed in the cytosol to support protein synthesis. Furthermore, since the enzyme systems of the general phenylpropanoid pathway and its specialized branches of secondary metabolism are located in the cytosol (17), aromatic amino acids (especially L-phenylalanine) are also required in the cytosol as initial substrates for secondary metabolism. The simplest possibility would be that a second, complete pathway of aromatic amino acid biosynthesis exists in the cytosol. Ample precedent has been established for duplicate, major biochemical pathways (glycolysis and oxidative pentose phosphate cycle) of higher plants that are separated from one another in the plastid and cytosolic compartments (18). Evidence to support the hypothesis for a cytosolic pathway (1,13) and the various approaches underway to prove or disprove the dual-pathway hypothesis are summarized in this paper. 

In a recent study (54), we showed increased activities of two enzymes of the general phenylpropanoid pathway, PAL and 4-coumarate CoA lig-ase, as well as one enzyme of the specific pathway of lignin biosynthesis, cinnamy 1-alcohol dehydrogenase (CAD), in resistant plants at the time of the hypersensitive host cell death. On the other hand, decreased activities were observed at the same time with susceptible host plants (54). Furthermore, we showed that the well known increase in peroxidase activities, which is strong in resistant and only weak in susceptible plants (55-58), is at least partly due to the increased activity of the lignin biosynthetic pathway (54,59). 

Rasmussen, S. and Dixon, R.A., Transgene-mediated and elicitor-induced perturbation of metabolic channeling at the entry point into the phenylpropanoid pathway. Plant Cell, 11, 1537, 1999. 

Blount, J.W. et ah, Altering expression of cinnamic acid 4-hydroxylase in transgenic plants provides evidence for a feedback loop at the entry point into the phenylpropanoid pathway. 

Loake, G.J. et al., Phenylpropanoid pathway intermediates regulate transient expression of a chalcone synthase gene promoter, Plant Cell, 3, 829, 1991. 

Yao, K.N., de Luca, V., and Brisson, N., Creation of a metabolic sink for tryptophan alters the phenylpropanoid pathway and the susceptibility of potato to Phytophthora infestans. Plant Cell, 1, 1787, 1995. 

Matsuda, F., Morino, K., Ano, R., Kuzawa, M., Wakasa, K., Miyagawa, H. (2005). Metabolic flux analysis of the phenylpropanoid pathway in elicitor-treated potato tuber tissue. Plant Cell Physiol., 46,454 66. 

Some of the pathways of animal and bacterial metabolism of aromatic amino acids also are used in plants. However, quantitatively more important are the reactions of the phenylpropanoid pathway,173-1743 which is initiated by phenylalanine ammonia-lyase (Eq. 14-45).175 As is shown at the top of Fig. 25-8, the initial product from phenylalanine is trails-cinnam-ate. After hydroxylation to 4-hydroxycinnamate (p-coumarate) and conversion to a coenzyme A ester,1753 the resulting p-coumaryl-CoA is converted into mono-, di-, and trihydroxy derivatives including anthocyanins (Box 21-E) and other flavonoid compounds.176 The dihydroxy and trihydroxy methylated products are the starting materials for formation of lignins and for a large series of other plant products, many of which impart characteristic fragrances. Some of these are illustrated in Fig. 25-8. 

Figure 25-8 Formation of some plant metabolites from phenylalanine and tyrosine via the phenylpropanoid pathway...

The phenylpropanoid pathway is the source of hundreds of metabolites that play critical roles in ensuring land plant survival, reproduction, and interaction... 

Deluc L, Barrieu F, Marchive C, Lauvergeat V, Decendit A, Richard T, Carde JP, Merillon JM, Hamdi S. 2006. Characterization of a grapevine R2R3-MYB transcription factor that regulates the phenylpropanoid pathway. Plant Physiol 140 499-511. 

Ro D-K, Douglas CJ. 2004. Reconstitution of the entry point of plant phenylpropanoid metabolism in yeast (Saccharomyces cerevisiae) Implication for control of metabolic flux into the phenylpropanoid pathway. J Biol Chem 279 2600-2607. 

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