Expression of Tryptophan Decarboxylase and Tyrosine Decarboxylase Genes in Tobacco Results in Altered Biochemical and Physiological Phenotypes

Abstract

The substrate specificity of tryptophan (Trp) decarboxylase (TDC) for Trp and tyrosine (Tyr) decarboxylase (TYDC) for Tyr was used to modify the in vivo pools of these amino acids in transgenic tobacco. Expression of TDC and TYDC was shown to deplete the levels of Trp and Tyr, respectively, during seedling development. The creation of artificial metabolic sinks for Trp and Tyr also drastically affected the levels of phenylalanine, as well as those of the non-aromatic amino acids methionine, valine, and leucine. Transgenic seedlings also displayed a root-curling phenotype that directly correlated with the depletion of the Trp pool. Nontransformed control seedlings could be induced to display this phenotype after treatment with inhibitors of auxin translocation such as 2,3,5-triiodobenzoic acid or N-1-naphthylphthalamic acid. The depletion of aromatic amino acids was also correlated with increases in the activities of the shikimate and phenylpropanoid pathways in older, light-treated transgenic seedlings expressing TDC, TYDC, or both. These results provide in vivo confirmation that aromatic amino acids exert regulatory feedback control over carbon flux through the shikimate pathway, as well as affecting pathways outside of aromatic amino acid biosynthesis.

Wound-Inducible Biosynthesis of Phytoalexin Hydroxycinnamic Acid Amides of Tyramine in Tryptophan and Tyrosine Decarboxylase Transgenic Tobacco Lines

“…2). In addition, the L-[5-3 H]Trp feeding experiment corroborated a previous study (Guillet et al, 2000) that only the two TDC-expressing lines accumulated severalfold higher levels of labeled tryptamine, compared to the wild-type and TYDC-expressing tobacco lines (Fig. 3A).…”

“…The area beyond the broken lines represents phenolic amides associated with the cell wall matrix, where R is H, OH, or OCH 3 depending if the phytoalexin amide is p = coumaroyltryamine, caffeoyltyramine, or feruloyltyramine. Transgenic tobaccos expressing TDC and/or TYDC make high levels of tryptamine and/or tyramine (Guillet et al, 2000). This hypothetical diagram also displays the possibility that transgenic plants expressing the TDC gene could also accumulate novel phenolic amides of tryptamine that are not known to occur in tobacco.…”

Coordinated Genetic Regulation of Growth and Lignin Revealed by Quantitative Trait Locus Analysis of cDNA Microarray Data in an Interspecific Backcross of Eucalyptus

“…The QTLs we identified here could represent such transcription factors. Alternatively, individual genes or clusters of genes could be directly involved through mechanisms such as feedback control, which is known to affect the shikimate and phenylpropanoid pathways (Blount et al, 2000;Guillet et al, 2000). Genetic mapping of candidate genes identified in this study revealed genetic colocalization of SAMS with growth and lignin gene expression QTLs.…”

Molecular Phenotyping of the pal1 and pal2 Mutants of Arabidopsis thaliana Reveals Far-Reaching Consequences on Phenylpropanoid, Amino Acid, and Carbohydrate Metabolism

“…The fact that the concentration of these amino acids increases, except for Met in the double mutant and Cys in pal1, suggests an overarching mechanism for homeostasis of amino acid levels that acts across individual biosynthetic pathways. Similarly, plants overexpressing a Trp or Tyr decarboxylase, thus artificially creating a metabolic sink, were altered in the aromatic and three nonaromatic amino acids (Yao et al, 1995;Guillet et al, 2000).…”