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.
Synonyms: indole-3-acetyl-N-amino acid-glucose synthesis, IAA conjugate biosynthesis II
|Superclasses:||Degradation/Utilization/Assimilation → Hormones Degradation → Plant Hormones Degradation → Auxins Degradation|
Some taxa known to possess this pathway include : Oryza sativa
Expected Taxonomic Range: Embryophyta
IAA (indole-3-acetic acid), one of the most common active forms of the phytohormone auxin, is often present in conjugated forms. Free IAA is involved in regulating many aspects of plant growth from embryogenesis to root and shoot development and reproduction. Meanwhile, conjugated forms of auxin play varied roles: some still have biological activity, others serve as inactive storage forms, and some appear to be permanently inactivated [Woodward05].
IAA-amino acid conjugates have been identified and studied in many species, including Arabidopsis thaliana [Woodward05], cucumber ( Cucumis sativus) [Sonner85], Scots pine ( Pinus sylvestris) [Ljung01], and rice Oryza sativa [Kai07, Matsuda05], and IAA-O-glucosyl esters have been encountered in multiple plant species, including, Arabidopsis and maize ( Zea mays) [Woodward05, Ehmann74]. But, there is now evidence concerning the biosynthesis of another conjugated form of IAA in rice that has a canonical O-linked amino acid adduct, and a less common N-linked glucose attached to the indole portion of IAA [Kai07] .
There is evidence for free IAA, IAA-aspartate, and IAA-glutamate in rice [Kai07, Matsuda05]. The simple reactions to form these two amino acid conjugates have been studied in Arabidopsis ( superpathway of indole-3-acetate conjugate biosynthesis) and most likely occur in a similar manner in rice. Now, radiotracer studies indicate that these IAA conjugates can be incorporated into IAA-Asp-N-glucose and IAA-Glu-N-glucose [Kai07]. Although UDP-glucose often participates in glucosyltransferase reactions the identity of the sugar donor in this reaction remains unknown. High levels of free IAA-N-glucose are detected in rice seeds, but, this compound does not appear to be a precursor for the glucosylated IAA-amino acid conjugates [Kai07]. In fact, it may actually be derived from these compounds through the action of an amide hydrolase. Alternatively, this compound may be produced by the N-glucosylation of IAA, a reaction that has been proposed to occur in Scots pine [Ljung01] seedlings.
Although these experiements only use one species, the presence of IAA-N-linked hexoses and/or IAA-N-linked-hexose-amino acid conjugates in other species such as Arabidopsis, maize, Lotus japonicus, and Scots pine [Ljung01, Kai07], suggests that these forms of auxin might be found throughout the plant kingdom. Neither IAA-N-glucose nor its amino acid conjugates show auxin activity in root and shoot elongation assays in rice [Kai07], and their biological role in auxin metabolism and auxin signaling needs to be clarified.
Variants: indole-3-acetate degradation I, indole-3-acetate degradation II, indole-3-acetate degradation III, indole-3-acetate degradation IV, indole-3-acetate degradation V, indole-3-acetate degradation VI, indole-3-acetate degradation VII, indole-3-acetate degradation VIII (bacterial)
Ehmann74: Ehmann A (1974). "Identification of 2-O (indole-3-acetyl)-D-glucopyranose, 4-O-(indole-3-acetyl)-D-glucopyranose and 6-O-(indole-3-acetyl)-D-glucopyranose from kernels of Zea mays by gas-liquid chromatography-mass spectrometry." Carbohydr Res 34(1);99-114. PMID: 4835696
Kai07: Kai K, Wakasa K, Miyagawa H (2007). "Metabolism of indole-3-acetic acid in rice: identification and characterization of N-beta-D-glucopyranosyl indole-3-acetic acid and its conjugates." Phytochemistry 68(20);2512-22. PMID: 17628621
Matsuda05: Matsuda F, Miyazawa H, Wakasa K, Miyagawa H (2005). "Quantification of indole-3-acetic acid and amino acid conjugates in rice by liquid chromatography-electrospray ionization-tandem mass spectrometry." Biosci Biotechnol Biochem 69(4);778-83. PMID: 15849417
Staswick05: Staswick PE, Serban B, Rowe M, Tiryaki I, Maldonado MT, Maldonado MC, Suza W (2005). "Characterization of an Arabidopsis enzyme family that conjugates amino acids to indole-3-acetic acid." Plant Cell 17(2);616-27. PMID: 15659623
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