Overexpression of arogenate dehydratase reveals an upstream point of metabolic control in phenylalanine biosynthesis

• Published in: The Plant journal : for cell and molecular biology Vol. 108; no. 3; pp. 737 - 751
• Main Authors: Yoo, Heejin, Shrivastava, Stuti, Lynch, Joseph H., Huang, Xing‐Qi, Widhalm, Joshua R., Guo, Longyun, Carter, Benjamin C., Qian, Yichun, Maeda, Hiroshi A., Ogas, Joseph P., Morgan, John A., Marshall‐Colón, Amy, Dudareva, Natalia
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.11.2021
• Subjects: Allosteric properties; Amino acids; arogenate dehydratase; Biosynthesis; Carbohydrate Epimerases - genetics; Carbohydrate Epimerases - metabolism; Dehydration; d‐ribulose‐5‐phosphate 3‐epimerase; Epimerase; Feedback; Feedback inhibition; Flowers; Flowers - genetics; Flowers - metabolism; Fluctuations; Gene Expression Regulation, Plant; Gene regulation; genes; Genetics; Hydro-Lyases - genetics; Hydro-Lyases - metabolism; Metabolic flux; metabolic flux analysis; Metabolism; Metabolites; Mutation; Pentose; pentose phosphate cycle; Pentose phosphate pathway; Petunia - genetics; Petunia - metabolism; Petunia hybrida; Phenolic compounds; Phenols; Phenylalanine; Phenylalanine - biosynthesis; Phenylalanine - metabolism; Plant Proteins - genetics; Plant Proteins - metabolism; Plants, Genetically Modified; Plastids; Plastids - genetics; Plastids - metabolism; reverse genetics; Secondary Metabolism - genetics; shikimate pathway; Shikimic Acid - metabolism; Transcription; transcription (genetics); Transcriptomics; Petunia hybrida; arogenate dehydratase; phenylalanine; phenylalanine biosynthesis; d-ribulose-5-phosphate 3-epimerase; shikimate pathway; pentose phosphate pathway
• ISSN: 0960-7412; 1365-313X; 1365-313X
• DOI: 10.1111/tpj.15467

SUMMARY Out of the three aromatic amino acids, the highest flux in plants is directed towards phenylalanine, which is utilized to synthesize proteins and thousands of phenolic metabolites contributing to plant fitness. Phenylalanine is produced predominantly in plastids via the shikimate pathway and subsequent arogenate pathway, both of which are subject to complex transcriptional and post‐transcriptional regulation. Previously, it was shown that allosteric feedback inhibition of arogenate dehydratase (ADT), which catalyzes the final step of the arogenate pathway, restricts flux through phenylalanine biosynthesis. Here, we show that in petunia (Petunia hybrida) flowers, which typically produce high phenylalanine levels, ADT regulation is relaxed, but not eliminated. Moderate expression of a feedback‐insensitive ADT increased flux towards phenylalanine, while high overexpression paradoxically reduced phenylalanine formation. This reduction could be partially, but not fully, recovered by bypassing other known metabolic flux control points in the aromatic amino acid network. Using comparative transcriptomics, reverse genetics, and metabolic flux analysis, we discovered that transcriptional regulation of the d‐ribulose‐5‐phosphate 3‐epimerase gene in the pentose phosphate pathway controls flux into the shikimate pathway. Taken together, our findings reveal that regulation within and upstream of the shikimate pathway shares control over phenylalanine biosynthesis in the plant cell. Significance Statement An increase in phenylalanine levels is a frequent target of metabolic engineering strategies for efficient production of phenylalanine‐derived metabolites. Phenylalanine is produced predominantly in plastids via the shikimate pathway and is subject to complex transcriptional and post‐transcriptional regulation, which occurs not only within the pathway but also upstream in the pentose phosphate pathway.