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Abstract l‐Tyrosine (Tyr) is an aromatic amino acid synthesized de novo in plants and microbes downstream of the shikimate pathway. In plants, Tyr and a Tyr pathway intermediate, 4‐hydroxyphenylpyruvate (HPP), are precursors to numerous specialized metabolites, which are crucial for plant and human health. Tyr is synthesized in the plastids by a TyrA family enzyme, arogenate dehydrogenase (ADH/TyrAa), which is feedback inhibited by Tyr. Additionally, many legumes possess prephenate dehydrogenases (PDH/TyrAp), which are insensitive to Tyr and localized to the cytosol. Yet the role of PDH enzymes in legumes is currently unknown. This study isolated and characterizedTnt1‐transposon mutants ofMtPDH1(pdh1) inMedicago truncatulato investigate PDH function. The pdh1mutants lackedPDHtranscript and PDH activity, and displayed little aberrant morphological phenotypes under standard growth conditions, providing genetic evidence thatMtPDH1is responsible for the PDH activity detected inM. truncatula. Though plant PDH enzymes and activity have been specifically found in legumes, nodule number and nitrogenase activity ofpdh1 mutants were not significantly reduced compared with wild‐type (Wt) during symbiosis with nitrogen‐fixing bacteria. Although Tyr levels were not significantly different between Wt and mutants under standard conditions, when carbon flux was increased by shikimate precursor feeding, mutants accumulated significantly less Tyr than Wt. These data suggest that MtPDH1 is involved in Tyr biosynthesis when the shikimate pathway is stimulated and possibly linked to unidentified legume‐specific specialized metabolism.
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This content will become publicly available on June 1, 2026
Maize big embryo 6 reveals roles of plastidial and cytosolic prephenate aminotransferases in seed and plant development
Abstract In plants, embryo size is determined via interactions between metabolic and developmental signals. Maize (Zea mays) big embryo 6 (bige6) enhances embryo size while sharply reducing plant growth. Here, we show that BigE6 encodes a plastidial prephenate aminotransferase (PPA-AT), a key enzyme in the arogenate pathway for L-phenylalanine (Phe) and L-tyrosine (Tyr) biosynthesis. The maize BigE6 paralog, BigE6Like, encodes a cytosol-localized PPA-AT, revealing Phe and Tyr biosynthesis via cytosolic arogenate as a potential alternative to the known cytosolic phenylpyruvate pathway. Moreover, the single PPA-AT gene of Arabidopsis (Arabidopsis thaliana) encodes plastidial and cytosolic enzymes by alternative splicing. Transgenic rescue of a ppa-at mutant in Arabidopsis demonstrates that the plastidial PPA-AT is indispensable for seed formation due, in part, to its essential role in the female gametophyte. Leaves of bige6 maize maintained overall homeostasis for aromatic amino acids and downstream metabolites, revealing a resilience of mechanisms that scale growth to a limiting supply of Phe and Tyr. In bige6 seeds, broad perturbation of amino acid homeostasis is associated with transcriptomic upregulation of growth processes in the embryo and endosperm, implicating amino acid signaling in the regulation of embryo size. Our findings reveal the complexity and developmental dependence of growth responses to limiting amino acid biosynthesis.
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- Award ID(s):
- 1748105
- PAR ID:
- 10613883
- Publisher / Repository:
- American Society of Plant Biologists
- Date Published:
- Journal Name:
- The Plant Cell
- Volume:
- 37
- Issue:
- 6
- ISSN:
- 1040-4651
- Subject(s) / Keyword(s):
- maize embryogenesis aromatic amino acid biosynthesis plant growth
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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