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 → Secondary Metabolites Biosynthesis → Phytoalexins Biosynthesis → Indole Phytoalexins Biosynthesis|
Some taxa known to possess this pathway include : Arabidopsis thaliana col
Expected Taxonomic Range: Brassicales
Camalexin is the main phytoalexin in Arabidopsis. It is involved in plant defense and has cancer-preventive property. The accumulation of camalexin in Arabidopsis is induced by a variety of microorganisms including bacteria, fungi and oomycetes.
Camalexin was previously proposed to be derived from indole-3-carboxaldehyde, independent of tryptophan. Recently, genetic evidence showed that camalexin is directly derived from tryptophan via indole-3-acetaldoxime, a branch point metabolite that also leads to the biosynthesis of secondary metabolites glucosinolates (glucosinolate biosynthesis from tryptophan) and the plant hormone IAA (indole-3-acetate biosynthesis II). Double-mutants of CYP79B2 and CYP79B3 were devoid of camalexin [Glawischnig04]. Indole-3-acetaldoxime is consequently converted to indole-3-acetonitrile (IAN) by CYP71A13 [Nafisi07].
In vivo feeding experiments suggested that the thiazole ring of camalexin is derived from cysteine [Zook97]. The exact steps of the thiazole ring formation remained elusive until recently. In a metabolomics study, the IAN conjugate Cys(IAN) was found to be an intermediate of camalexin biosynthesis. The formation of Cys(IAN) possibly proceeds via intermediates γGluCYs(IAN)Gly and γGluCYs(IAN). Accumulation of these three compounds was detected in CYP71B15 mutants in an in vivo feeding experiment [Bolduc09]. CYP71B15 was previously shown to catalyze the last step of camalexin biosynthesis, converting dihydrocamalexin (DHCA) to camalexin. CYP71B15 is a novel plant enzyme in that it is the only known cytochrome P450 in plants results in simultaneous decarboxylation and introduction of a C-C double bond [Schuhegger06]. More interestingly, CYP71B15 is recently found a multifunctional enzyme that also catalyzes the NADPH-dependent conversions of Cys(IAN) to DHCA [Bottcher09]. During the conversion of one molecule Cys(IAN) to DHCA, one molecule of cyanide is released. In planta accumulation of cyanide may shut down the CYP P450 catalyzed camalexin biosynthesis process and thus cyanide is possibly detoxified via the cyanide detoxification pathway (cyanide detoxification I).
The biosynthetic pathway is coordinately induced, strictly localized to the site of pathogen infection [Glawischnig06].
Unification Links: AraCyc:CAMALEXIN-SYN
Bottcher09: Bottcher C, Westphal L, Schmotz C, Prade E, Scheel D, Glawischnig E (2009). "The multifunctional enzyme CYP71B15 (PHYTOALEXIN DEFICIENT3) converts cysteine-indole-3-acetonitrile to camalexin in the indole-3-acetonitrile metabolic network of Arabidopsis thaliana." Plant Cell 21(6);1830-45. PMID: 19567706
Glawischnig04: Glawischnig E, Hansen BG, Olsen CE, Halkier BA (2004). "Camalexin is synthesized from indole-3-acetaldoxime, a key branching point between primary and secondary metabolism in Arabidopsis." Proc Natl Acad Sci U S A 101(21);8245-50. PMID: 15148388
Nafisi07: Nafisi M, Goregaoker S, Botanga CJ, Glawischnig E, Olsen CE, Halkier BA, Glazebrook J (2007). "Arabidopsis cytochrome P450 monooxygenase 71A13 catalyzes the conversion of indole-3-acetaldoxime in camalexin synthesis." Plant Cell 19(6);2039-52. PMID: 17573535
Schuhegger06: Schuhegger R, Nafisi M, Mansourova M, Petersen BL, Olsen CE, Svatos A, Halkier BA, Glawischnig E (2006). "CYP71B15 (PAD3) catalyzes the final step in camalexin biosynthesis." Plant Physiol 141(4);1248-54. PMID: 16766671
Hull00: Hull AK, Vij R, Celenza JL (2000). "Arabidopsis cytochrome P450s that catalyze the first step of tryptophan-dependent indole-3-acetic acid biosynthesis." Proc Natl Acad Sci U S A 2000;97(5);2379-84. PMID: 10681464
Mikkelsen00: Mikkelsen MD, Hansen CH, Wittstock U, Halkier BA (2000). "Cytochrome P450 CYP79B2 from Arabidopsis catalyzes the conversion of tryptophan to indole-3-acetaldoxime, a precursor of indole glucosinolates and indole-3-acetic acid." J Biol Chem 275(43);33712-7. PMID: 10922360
Naur03: Naur P, Hansen CH, Bak S, Hansen BG, Jensen NB, Nielsen HL, Halkier BA (2003). "CYP79B1 from Sinapis alba converts tryptophan to indole-3-acetaldoxime." Arch Biochem Biophys 409(1);235-41. PMID: 12464264
Zhao02a: Zhao Y, Hull AK, Gupta NR, Goss KA, Alonso J, Ecker JR, Normanly J, Chory J, Celenza JL (2002). "Trp-dependent auxin biosynthesis in Arabidopsis: involvement of cytochrome P450s CYP79B2 and CYP79B3." Genes Dev 16(23);3100-12. PMID: 12464638
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