Phenylpropanoids biosynthetic genes

Sablowski, R. W., Moyano, E., Culianez-Macia, F. A., Schuch, W., Martin, C., and Bevan, M., 1994. A flower-specific Myb protein activates transcription of phenylpropanoid biosynthetic genes, EMBO J. 13 128-137. 

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. 

Fig. 1. Simplified diagram of the phenylpropanoid and flavonoid biosynthetic pathways. Enzymes that catalyze the reactions are placed on the left-hand side, and transcription factors on the right-hand side of the arrows. Both transcription factors for which their control over the enzymatic steps has been genetically proven, as well as transcription factors that have been shown to interact with promoters of the structural genes, are shown. PAL Phenylalanine ammonia lyase C4H cinnamate 4-hydroxylase 4CL 4-coumaroyl-coenzyme A ligase CHS chalcone synthase CHI chalcone-flavanone isomerase F3H flavanone 3(3-hydroxylase DFR dihydroflavonol 4-reductase AS anthocyanin synthase UFGT UDP glucose-flavonol glucosyl transferase RT anthocyanin rhamnosyl transferase...

In the phenylpropanoid pathway, the first biosynthetic step leading to SA is a deamination of phenylalanine to CA which is catalyzed by phenylalanine ammonia lyase (PAL). This enzyme is induced by a range of biotic and abiotic stress conditions and is a key regulator in the phenylpropanoid pathway, which yields a variety of phenolics among others involved in structural and defense-related functions [42]. In recent years, PAL and its corresponding genes have been subject of numerous studies in various plant species [43 7]. 

In a similar study, different phenylpropanoid acids, such as cinnamic acid (32), p-coumaric acid (33), caffeic acid (34), and ferulic acid (35), were fed to recombinant yeast containing four different initial flavanone biosynthetic plant genes, C4H, 4CL, CHS, and CHI, at different time intervals to produce flavanones. In cinnamic acid-supplemented culture, 16.3 mg 1 of pinocembrin (31) and 0.2 mg 1 of naringenin (30) were produced. Naringenin (28.3 mg 1 ) and (2S)-eriodictyol (6.5 mg 1 ) were detected in p-coumaric acid- and caffeic acid-supplemented cultures, respectively. No flavanones were produced with ferulic acid precursor substrate [33]. The production of pinocembrin and naringenin in S. cerevisiae was 22- and 62-fold higher compared to that of respective flavanones in E. coli [34]. 

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