This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Aromatic Compounds Biosynthesis|
Expected Taxonomic Range: Embryophyta
Plants must confront many different dangerous xenobiotic compounds in their environments. Often, plant enzymes modify these compounds to change their reactivity and/or subcellular localization in order to render them less toxic [Taguchi10]. Glycosylation, glutathione conjugation, sulfonylation, and other modifications have been observed in many plant species and their role in detoxification has been compared to xenobiotic modifications that take place in the liver [Sandermann94]. Sometimes, multiple modifications may be introduced sequentially, such as the glycosylation followed by malonylation depicted in this pathway [Matern83a, Sandermann91, Taguchi10, Suzuki01b].
About This Pathway
Naphthols are phenolic xenobiotic compounds that may be encountered in the soil by plants. Studies on tobacco cultured cells indicate that naphthols are harmful. Not surprisingly, tobacco, as well as several other plant species, including Arabidopsis thaliana, Medicago truncatula, and Oryza sativa (rice) modify naphthols forming compounds such as 2-naphthol 6'-O-malonylglucoside [Taguchi03, Taguchi05, Taguchi10].
In this pathway, glucosyl moieties are first introduced by glucosyltransferases. When plants are grown in liquid media, glucosylated naphthols are excreted into the solution by some plant species, including Arabidopsis and tobacco [Taguchi10]. However, malonyltransferases, such as two enzymes identified in Arabidopsis (PMaT1 and PMaT2) and one in tobacco can further modify the glucosylated naphthols to produce malonylated glucosides . In contrast to the glucosides, these doubly modified compounds appear to be retained within plants, presumably within the vacuole [Taguchi10]. The compounds present in this pathway represent a subset of the products that can be formed by PMaT1 and PMaT2 in vitro. Further work will be required to understand the biologically relevant substrates of these enzymes and to gain a better understanding of how both glycosylation and subsequent malonylation of compounds contribute to plant defense against both xenobiotics and endogenously produced harmful compounds [Taguchi10].
Matern83a: Matern U, Heller W, Himmelspach K (1983). "Conformational changes of apigenin 7-O-(6-O-malonylglucoside), a vacuolar pigment from parsley, with solvent composition and proton concentration." Eur J Biochem 133(2);439-48. PMID: 6303788
Sandermann91: Sandermann H, Schmitt R, Eckey H, Bauknecht T (1991). "Plant biochemistry of xenobiotics: isolation and properties of soybean O- and N-glucosyl and O- and N-malonyltransferases for chlorinated phenols and anilines." Arch Biochem Biophys 287(2);341-50. PMID: 1832837
Suzuki01b: Suzuki H, Nakayama T, Yonekura-Sakakibara K, Fukui Y, Nakamura N, Nakao M, Tanaka Y, Yamaguchi MA, Kusumi T, Nishino T (2001). "Malonyl-CoA:anthocyanin 5-O-glucoside-6"'-O-malonyltransferase from scarlet sage (Salvia splendens) flowers. Enzyme purification, gene cloning, expression, and characterization." J Biol Chem 276(52);49013-9. PMID: 11598135
Taguchi03: Taguchi, G., Nakamura, M., Hayashida, N., Okazaki, M. (2003). "Exogenously added naphthols induce three glucosyltransferases, and are accumulated as glucosides in tobacco cells ." Plant Science. 164(1):231-240.
Taguchi05: Taguchi G, Shitchi Y, Shirasawa S, Yamamoto H, Hayashida N (2005). "Molecular cloning, characterization, and downregulation of an acyltransferase that catalyzes the malonylation of flavonoid and naphthol glucosides in tobacco cells." Plant J 42(4);481-91. PMID: 15860007
Taguchi10: Taguchi G, Ubukata T, Nozue H, Kobayashi Y, Takahi M, Yamamoto H, Hayashida N (2010). "Malonylation is a key reaction in the metabolism of xenobiotic phenolic glucosides in Arabidopsis and tobacco." Plant J 63(6);1031-41. PMID: 20626660
Rubio06: Rubio S, Larson TR, Gonzalez-Guzman M, Alejandro S, Graham IA, Serrano R, Rodriguez PL (2006). "An Arabidopsis mutant impaired in coenzyme A biosynthesis is sugar dependent for seedling establishment." Plant Physiol 140(3);830-43. PMID: 16415216
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