Biosynthesis of the Halogenated Auxin, 4-Chloroindole-3-Acetic Acid

Tivendale, Nathan D.; Davidson, Sandra E.; Davies, Noel W.; Smith, Jason A.; Quittenden, Laura J.; Sutton, Lily; Bala, Raj Kiran; Signor, Christine Le; Thompson, Richard J.; Horne, James; Reid, James B.; Ross, John J.

doi:10.1104/pp.112.198457

Cited by 70 publications

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“…2 However, a second bioactive auxin, 4-Cl-IAA, predominates during the later stages of seed development. Metabolism experiments demonstrate that the chlorine is not introduced after the formation of IAA, and it was therefore of paramount importance to determine whether the pea aminotransferases can also utilize 4-chlorotryptophan.…”

Section: A Mutation Affecting the Synthesis Of 4-chloroindole-3-acetimentioning

confidence: 99%

“…Metabolism experiments also ruled out the indole-3-acetamide pathway (see Fig. 1), 2 while a fourth tryptophan-dependent pathway, via indole-3-acetaldoxime (see Fig. 1), is thought not to operate outside the Brassicaceae.…”

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“…We cloned three aminotransferase genes from pea and showed that two of the encoded enzymes convert tryptophan to IPyA, which is then converted in some way to IAA. 2 In pea seeds IAA is the most abundant auxin traditionally, schemes depicting auxin biosynthesis in plants have been notoriously complex. they have involved up to four possible pathways by which the amino acid tryptophan might be converted to the main active auxin, indole-3-acetic acid (iaa), while another pathway was suggested to bypass tryptophan altogether.…”

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confidence: 99%

“…2 Pea seeds are an excellent system for studying the metabolism of potential auxin intermediates. They are large, and labeled compounds can be injected into the seeds either in situ or after they are excised and placed in vitro.…”

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A mutation affecting the synthesis of 4-chloroindole-3-acetic acid

Ross

Tivendale

Davidson

et al. 2012

Plant Signaling & Behavior

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Evidence for the IPyA pathway in pea seeds comes from metabolism experiments with labeled compounds, the isolation of genes, and the effects of a mutation in one of those genes.2 Pea seeds are an excellent system for studying the metabolism of potential auxin intermediates. They are large, and labeled compounds can be injected into the seeds either in situ or after they are excised and placed in vitro. Typically, potential intermediates are injected at the liquid endosperm stage, and their subsequent metabolism determined by mass spectrometry. Additional compounds are injected into separate seeds as controls. For example, to test whether the tryptamine pathway operates in pea seeds, (see Fig. 1) labeled tryptamine was injected. Labeled tryptophan was injected into separate control seeds.3 Label was detected in IAA in the latter but not the former case, indicating that tryptamine is not an intermediate between tryptophan and IAA in this system. The lack of conversion of tryptamine to IAA cannot be attributed to wounding caused by the injection, because tryptophan was converted to IAA. Metabolism experiments also ruled out the indole-3-acetamide pathway (see Fig. 1), 2 while a fourth tryptophan-dependent pathway, via indole-3-acetaldoxime (see Fig. 1), is thought not to operate outside the Brassicaceae. When it became clear that the tryptamine pathway does not operate in pea seeds 3 (although it can operate in roots 5 ), we decided to investigate the IPyA pathway. We cloned three aminotransferase genes from pea and showed that two of the encoded enzymes convert tryptophan to IPyA, which is then converted in some way to IAA.2 In pea seeds IAA is the most abundant auxin traditionally, schemes depicting auxin biosynthesis in plants have been notoriously complex. they have involved up to four possible pathways by which the amino acid tryptophan might be converted to the main active auxin, indole-3-acetic acid (iaa), while another pathway was suggested to bypass tryptophan altogether. it was also postulated that different plants use different pathways, further adding to the complexity. in 2011, however, it was suggested that one of the four tryptophan-dependent pathways, via indole-3-pyruvic acid (iPya), is the main pathway in Arabidopsis thaliana, 1 although concurrent operation of one or more other pathways has not been excluded. We recently showed that, for seeds of Pisum sativum (pea), it is possible to go one step further.2 our new evidence indicates that the iPya pathway is the only tryptophan-dependent iaa synthesis pathway operating in pea seeds. We also demonstrated that the main auxin in developing pea seeds, 4-chloroindole-3-acetic acid (4-Cl-iaa), which accumulates to levels far exceeding those of iaa, is synthesized via a chlorinated version of the iPya pathway.

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Section: A Mutation Affecting the Synthesis Of 4-chloroindole-3-acetimentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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A mutation affecting the synthesis of 4-chloroindole-3-acetic acid

Ross

Tivendale

Davidson

et al. 2012

Plant Signaling & Behavior

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“…3 Recent metabolism experiments demonstrated that 4-Cl-IAA is synthesized via a chlorinated version of the indole-3-pyruvate pathway, the main tryptophan-dependent IAA synthesis pathway operating in pea seeds. 4 The growth regulatory role of chlorinated auxin is thought to involve the induction of GA biosynthesis and the inhibition of ethylene action on early pericarp growth and elongation. 5 The phylogenetic distribution and evolutionary origins of this hormone, however, have received little attention.…”

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confidence: 99%