The pathway of auxin biosynthesis in ..
The main auxin biosynthesis pathway in Arabidopsis
The main auxin biosynthesis pathway in ..
Indole-3-acetic acid (IAA), the naturally occurring major species of auxins in plants, can be synthesized through the precursor tryptophan (Trp) known as the Trp-dependent IAA biosynthetic pathway.
Diverse bacterial species possess the ability to produce the auxin(indole-3-acetic acid, IAA, phyto-hormone). Different biosynthesis pathways have been identified and redundancy for IAA biosynthesis is widespread among plant-associated bacteria. A high degree of similarity between IAA biosynthesis pathways in plants and bacteria was observed. 
This two-step auxin biosynthesis pathway is highly conserved ..
Here, we provide genetic, enzymatic, and metabolite-based evidence that TAA and YUC families function in the same auxin biosynthetic pathway (). YUC is implicated in the conversion of IPA to IAA in Arabidopsis. IAAld is probably not a precursor of IAA in the IPA pathway. We conclude that YUC family catalyzes a rate-limiting step of the IPA pathway that produces IAA essential for plant development.
To investigate whether TAA and YUC families act in the same pathway, we generated estradiol (Est)-inducible TAA1 overexpression plants in Arabidopsis WT (TAA1ox) and yuc1D (TAA1ox yuc1D), respectively. We predicted that cooverexpression of TAA1 genes would enhance IAA biosynthesis in yuc1D mutants if TAA1 and YUC1 act in the same pathway. TAA1ox plants did not show apparent phenotypes relative to vector control plants (pER8) on Murashige–Skoog agar media containing Est ( and ). This observation strengthens the result of Tao et al. that TAA1 does not mediate a rate-limiting step in IAA biosynthesis (). We found that the formation of adventitious and lateral roots was significantly enhanced in TAA1ox yuc1D plants relative to that in yuc1D mutants ( and ). To determine if overexpression of TAA1 enhances IAA biosynthesis in yuc1D mutants, we analyzed IAA levels in these mutants by liquid chromatography–electrospray ionization–tandem MS (LC-ESI-MS/MS). We also analyzed the levels of two IAA–amino acid conjugates, IAA-aspartate (IAA-Asp) and IAA-glutamate (IAA-Glu). IAA is metabolized to IAA-Asp, IAA-Glu, and other amino acid conjugates by the GH3 family for homeostatic regulation of auxin in plants () (). Hence, the GH3 family may greatly contribute to maintaining the level of IAA if excess amounts of IAA were produced in TAA1ox yuc1D mutants. As shown in , IAA level increased slightly, but IAA-Asp and IAA-Glu levels did not change, in TAA1ox compared with that in pER8. In yuc1D mutants, IAA levels were not affected, but IAA-Glu levels increased by 6.8 times. We found that both IAA and IAA-Glu levels were 1.5 times and 2.3 times elevated, respectively, in TAA1ox yuc1D relative to that in yuc1D (). This suggests that GH3 family possibly metabolized excess amounts of IAA in these mutants. A significant increase in total levels of IAA and IAA-Glu in TAA1ox yuc1D relative to yuc1D indicates that TAA1 and YUC1 act synergistically to enhance IAA biosynthesis in Arabidopsis.
Biosynthesis, Metabolism and Signaling Pathway of Auxin …
The YUC pathway has been proposed as a common IAA biosynthetic pathway that produces auxin essential for embryogenesis, flower development, seedling growth, and vascular patterning (–). YUC genes have been identified ubiquitously in various plant species (). In maize, a monocot-specific YUC-like protein SPARSE INFLORESCENCE 1 (SPI1) plays critical roles in vegetative and reproductive development (). YUC family encode flavin monooxygenase-like proteins that catalyze a rate-limiting step in IAA biosynthesis (). Arabidopsis yuc1D mutants, in which YUC1 is expressed under the control of cauliflower mosaic virus 35S promoter, show slightly increased IAA levels along with high-auxin phenotypes such as elongated hypocotyls, epinastic leaves, and enhanced apical dominance (). Arabidopsis has 11 YUC genes, and yuc multiple KO mutants show severe auxin-deficient phenotypes (, ). YUC catalyzes the conversion of tryptamine (TAM) to N-hydroxy-TAM (HTAM) in vitro (, ). IAOx and indole-3-acetonitrile (IAN) were previously proposed as possible intermediates in the conversion of HTAM to IAA (). However, our previous study indicated that IAOx and IAN are not common intermediates of IAA biosynthesis in plants (). The underlying pathway from HTAM to IAA is still unknown.
More recent studies have isolated three Arabidopsis mutants—shade avoidance 3, weak ethylene insensitive 8 (wei8), and transport inhibitor response 2—in which the TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 (TAA1) gene is disrupted (–). TAA1 mediates the conversion of Trp to IPA in the first step of the IPA pathway (). TAA1 plays critical roles in embryogenesis, flower development, seedling growth, vascular patterning, lateral root formation, tropism, shade avoidance, and temperature-dependent hypocotyl elongation (–). There are two TAA1-related proteins—TAR1 and TAR2—in Arabidopsis. Double-KO mutants of TAA1 and TAR2 genes, wei8 tar2, showed severe growth defects caused by a significant reduction of IAA production in Arabidopsis (). In maize, VANISHING TASSEL 2 (VT2) gene has been identified to encode a grass-specific TAA1 coorthologue required for vegetative and reproductive development (). The pathway from IPA to IAA via indole-3-acetaldehyde (IAAld) by IPA DECARBOXYLASE (IPD) and ALDEHYDE OXIDASE (AO) has been proposed (, , ). However, IPD genes have not yet been identified in plants. There are four AO genes in Arabidopsis. It has been demonstrated that ARABIDOPSIS ALDEHYDE OXIDASE 1 (AAO1) can convert IAAld to IAA () (). AO family requires a molybdenum cofactor sulfurase encoded by ABA DEFICIENT 3 (ABA3) for its enzyme activity (, ). However, as aba3-deficient mutants do not show an apparent auxin-deficient phenotype, it is not clear whether the AO family actually participates in IAA biosynthesis in plants.
Researchers clarify main auxin biosynthesis pathway | …
Auxin biosynthesis pathway pdf995 - Clash Royale …
The Pathway of Auxin Biosynthesis in Plants - Download as PDF File (.pdf), Text File (.txt) or read online. auksin
The main auxin biosynthesis pathway in Arabidopsis | …
The successful elucidation of a complete auxin biosynthesis pathway provides the necessary tools for ..
What is the tryptophan-dependent pathway in auxin synthesis?
Rapid Synthesis of Auxin via a New Tryptophan-Dependent Pathway Is Required for Shade Avoidance in Plants
The pathway of auxin biosynthesis in plants (pdf) | …
The IPA and YUC pathways have been proposed to independently produce IAA (). However, the phenotypic similarities between TAA-deficient and YUC-deficient mutants suggested that TAA and YUC families possibly operate in the same auxin biosynthetic pathway (, ). A recent genetic study in maize led to the proposal that VT2 and SPI1, coorthologues of TAA and YUC, may function in the same IAA biosynthetic pathway, as there was no significant change in IAA levels between vt2 spi1 double mutants and vt2 single mutants ().
This pathway involves the protein ..
Auxin plays fundamental roles in plant growth and development. Auxin regulates cell division, cell expansion, cell differentiation, lateral root formation, flowering, and tropic responses (). After the discovery of indole-3-acetic acid (IAA) in the 1930s, auxin has been virtually synonymous with IAA for more than 70 y. Recent studies demonstrated that IAA directly interacts with the F-box protein TIR1, and promotes the degradation of the Aux/IAA transcriptional repressors to activate diverse auxin responsive genes (–). Despite the importance of IAA in plants, IAA biosynthesis is not fully understood, most likely because of the existence of multiple pathways and functional redundancy of enzymes within the pathway (, ).
AUXIN BIOSYNTHESIS | Annual Review of Plant Biology
The phytohormone auxin plays critical roles in the regulation of plant growth and development. Indole-3-acetic acid (IAA) has been recognized as the major auxin for more than 70 y. Although several pathways have been proposed, how auxin is synthesized in plants is still unclear. Previous genetic and enzymatic studies demonstrated that both TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA) and YUCCA (YUC) flavin monooxygenase-like proteins are required for biosynthesis of IAA during plant development, but these enzymes were placed in two independent pathways. In this article, we demonstrate that the TAA family produces indole-3-pyruvic acid (IPA) and the YUC family functions in the conversion of IPA to IAA in Arabidopsis (Arabidopsis thaliana) by a quantification method of IPA using liquid chromatography–electrospray ionization–tandem MS. We further show that YUC protein expressed in Escherichia coli directly converts IPA to IAA. Indole-3-acetaldehyde is probably not a precursor of IAA in the IPA pathway. Our results indicate that YUC proteins catalyze a rate-limiting step of the IPA pathway, which is the main IAA biosynthesis pathway in Arabidopsis.
08/11/2011 · National Academy of Sciences
These discoveries pave an avenue for elucidating the Trp-independent auxin biosynthetic pathway and its functions in regulating plant growth and development, thereby making a solid conclusion on a long-lasting debate in auxin biology.
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