Role of cytosolic, tyrosine‐insensitive prephenate dehydrogenase in Medicago truncatula
Role of cytosolic, tyrosine‐insensitive prephenate dehydrogenase in Medicago truncatula
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胞质、酪氨酸不敏感的预苯酸脱氢酶在蒺藜苜蓿中的作用
DOI：
10.1002/pld3.218
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发表时间：
2020
期刊：
影响因子：
3
通讯作者：
Maeda, Hiroshi A.
中科院分区：
文献类型：
--
作者：
Schenck, Craig A.;Westphal, Josh;Jayaraman, Dhileepkumar;Garcia, Kevin;Wen, Jiangqi;Mysore, Kirankumar S.;Ané, Jean‐Michel;Sumner, Lloyd W.;Maeda, Hiroshi A.
L酪氨酸(Tyr)是莽草酸途径下游植物和微生物中从头合成的一种芳香族氨基酸。在植物中，Tyr和Tyr途径的中间体4-羟基苯基丙酮酸(HPP)是许多特定代谢物的前体，这些代谢物对植物和人类健康至关重要。酪氨酸脱氢酶(ADH/TyrAa)是一种酪氨酸脱氢酶(ADH/TyrAa)，由Tyr家族的反馈抑制酶在叶绿体中合成。此外，许多豆科植物具有预苯酸脱氢酶(PDH/TyrAp)，它对Tyr不敏感，定位于细胞质。然而，PDH酶在豆类中的作用目前尚不清楚。本研究分离并鉴定了MtPDH1(Pdh1)的Tnt1-转座子突变体，以研究PDH的功能。Pdh1突变体缺乏PDH转录本和PDH活性，在标准生长条件下几乎没有表现出异常的形态表型，这提供了MtPDH1与在元宝菇中检测到的PDH活性有关的遗传证据。虽然植物PDH酶和活性在豆科植物中是特异的，但在与固氮菌共生的过程中，pdh1突变体的根瘤数和固氮酶活性与野生型(Wt)相比并没有显著降低。尽管在标准条件下突变体和突变体的Tyr水平没有显著差异，但当通过莽草酸盐前体补给增加碳通量时，突变体积累的Tyr显著少于Wt。这些数据表明，当莽草酸途径受到刺激时，MtPDH1参与了Tyr的生物合成，并可能与未知的豆科植物特有的专门化代谢有关。
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. Thepdh1mutants 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 ofpdh1mutants 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.