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/TyrA_a), which is feedback inhibited by Tyr. Additionally, many legumes possess prephenate dehydrogenases (PDH/TyrA_p), 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 characterized Tnt1‐transposon mutants of MtPDH1 (pdh1) in Medicago truncatula to investigate PDH function. The pdh1 mutants lacked PDH transcript and PDH activity, and displayed little aberrant morphological phenotypes under standard growth conditions, providing genetic evidence that MtPDH1 is responsible for the PDH activity detected in M. truncatula. Though plant PDH enzymes and activity have been specifically found in legumes, nodule number and nitrogenase activity of pdh1 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.

中文翻译：

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胞嘧啶，酪氨酸不敏感的苯甲酸酯脱氢酶在in藜苜蓿中的作用。

l酪氨酸（Tyr）是the草酸酯途径下游植物和微生物中从头合成的芳香族氨基酸。在植物中，Tyr和一个Tyr途径中间体4-羟基苯丙酮酸（HPP）是许多专​​门代谢产物的前体，这些代谢产物对植物和人类健康至关重要。Tyr是通过TyrA家族酶，即Arogenate脱氢酶（ADH / TyrA _a）在质体中合成的，该酶被Tyr反馈抑制。另外，许多豆类都具有苯甲酸酯脱氢酶（PDH / TyrA _p），它们对Tyr不敏感，并局限于细胞质。目前尚不清楚PDH酶在豆类中的作用。本研究分离和表征TNT1的-transposon突变体MtPDH1（PDH1）在Medicago truncatula中研究PDH功能。所述 PDH1突变体缺乏PDH转录和PDH活性，并在标准生长条件下显示小异常形态学表型，提供遗传证据表明MtPDH1负责检测出的PDH活性蒺藜苜蓿。尽管在豆类中特别发现了植物PDH酶和活性，但pdh1的根瘤数和固氮酶活性却很高 与固氮细菌共生期间，野生型（Wt）突变体没有明显减少。尽管在标准条件下Wt和突变体之间的Tyr水平没有显着差异，但是当通过sh草酸酯前体进料增加碳通量时，突变体的Tyr累积量明显少于Wt。这些数据表明，当刺激the草酸酯途径时，MtPDH1参与了Tyr的生物合成，并且可能与未鉴定的豆类特异性专业代谢有关。