Aromatic Amino Acid Biosynthesis Pathways in Plants

Aromatic amino acids—phenylalanine, tyrosine and tryptophan—are synthesised in plants via the shikimate pathway, a high‐flux series of reactions that channels carbon from photosynthesis into a uniform intermediate, chorismate. From chorismate, distinct branch points lead to the three aromatic amino acids. Phenylalanine is formed predominantly via the plastidial arogenate pathway, whereas tyrosine arises through transamination of prephenate. An alternative phenylpyruvate pathway operates in the cytosol, illustrating subcellular partitioning of aromatic amino acid biosynthesis. Enzyme isoforms such as chorismate mutases, prephenate dehydratases and aminotransferases orchestrate flux distribution between primary metabolism and specialised metabolites. The pathway underpins production of lignin, flavonoids, alkaloids and other phenylpropanoids that drive plant growth, defence and ecological interactions. Regulation occurs through allosteric feedback, transcriptional control and compartmental trafficking of intermediates. Recent advances have revealed complex isoform coordination at entry and exit steps, and export mechanisms that balance plastidial synthesis with cytosolic demand. Understanding this network informs bioengineering efforts to enhance stress tolerance, optimise biomass composition and produce high‐value natural products.

Research from Nature Portfolio

Recent studies have elucidated how grasses maintain high production of both tyrosine and phenylalanine to feed a dual lignin pathway. Stable-isotope labelling combined with in vitro enzyme assays demonstrated that specific enzyme isoforms at the entry (chorismate mutases) and exit (prephenate dehydratases) steps are coordinately expressed, enabling grasses to produce tyrosine tenfold faster than Arabidopsis without compromising phenylalanine biosynthesis. This coordination highlights novel targets for metabolic engineering of lignocellulosic crops.

Completion of the cytosolic phenylpyruvate pathway has revealed that plants possess a microbial‐like route for phenylalanine biosynthesis outside the plastid. A cytosolic chorismate mutase directs flux towards phenylpyruvate, and an alternative transcription start site yields a prephenate dehydratase that functions in the cytosol. This discovery completes the delineation of phenylalanine synthesis via phenylpyruvate, demonstrating that the cytosol is an active site of aromatic amino acid production.

Identification of a plastidial phenylalanine exporter has shown that a dedicated transporter regulates flux through the aromatic amino‐acid network. Manipulation of this transporter alters levels of phenylalanine and its derived volatiles, confirming that export rate from plastids contributes to overall pathway regulation and offers a means to redirect carbon into value‐added phenylpropanoids.

Aromatic Amino Acid Biosynthesis Pathways in Plants publication trend

The graph below shows the total number of articles in aromatic amino acid biosynthesis pathways in plants across all publications each year (not limited to Nature Index journals).

Technical terms

Shikimate pathway: A series of enzymatic reactions converting phosphoenolpyruvate and erythrose-4-phosphate into chorismate, the common precursor to all aromatic amino acids.

Chorismate: The end product of the shikimate pathway that serves as a branching point for phenylalanine, tyrosine and tryptophan biosynthesis.

Arogenate pathway: A plastidial route to phenylalanine involving conversion of prephenate to arogenate and subsequent dehydration.

Phenylpyruvate pathway: A cytosolic pathway in which chorismate is converted to prephenate, then to phenylpyruvate and finally to phenylalanine.

Chorismate mutase: An enzyme that converts chorismate to prephenate, directing flux into aromatic amino acid branches.

Phenylpropanoids: A diverse class of secondary metabolites derived from phenylalanine, including lignin, flavonoids and other compounds involved in defence and structural integrity.

References

1. Coordinated regulation of the entry and exit steps of aromatic amino acid biosynthesis supports the dual lignin pathway in grasses. Nature Communications (2023).
2. Completion of the cytosolic post-chorismate phenylalanine biosynthetic pathway in plants. Nature Communications (2019).
3. Identification of a plastidial phenylalanine exporter that influences flux distribution through the phenylalanine biosynthetic network. Nature Communications (2015).
4. Biosynthesis and Metabolic Fate of Phenylalanine in Conifers. Frontiers in Plant Science (2016).
5. The entry reaction of the plant shikimate pathway is subjected to highly complex metabolite-mediated regulation. The Plant Cell (2021).
6. Enhanced Production of Aromatic Amino Acids in Tobacco Plants Leads to Increased Phenylpropanoid Metabolites and Tolerance to Stresses. Frontiers in Plant Science (2021).