Departamento de Biología Molecular y Bioquímica, Universidad de Málaga, Málaga, Spain.
Plant Cell Physiol. 2018 Dec 1;59(12):2409-2420. doi: 10.1093/pcp/pcy200.
Phenylalanine (Phe) biosynthesis in plants is a key process, as Phe serves as a precursor of proteins and phenylpropanoids. The prephenate pathway connects chorismate, the final product of the shikimate pathway, with the biosynthesis of Phe and tyrosine. Two alternative routes of Phe biosynthesis have been reported: one depending on arogenate, and the other on phenylpyruvate. Whereas the arogenate pathway is considered the main route, the role of the phenylpyruvate pathway remains unclear. Here, we report that a deficiency in ADT2, a bifunctional arogenate dehydratase (ADT)/prephenate dehydratase (PDT) enzyme, causes embryo arrest and seed abortion. This result makes a clear distinction between the essential role of ADT2 and the five remaining ADT genes from Arabidopsis, which display mostly overlapping functions. We have found that PHA2, a monofunctional PDT from yeast, restores the adt2 phenotype when it is targeted within the plastids, but not when is expressed in the cytosol. Similar results can be obtained by expressing ADT3, a monofunctional ADT. These results suggest that Phe can be synthesized from phenylpyruvate or arogenate when the bifunctional ADT2 is replaced by other ADT or PDT enzymes during seed formation, highlighting the importance of Phe biosynthesis for embryo development, and providing further insights into the plasticity of Phe biosynthesis.
植物中的苯丙氨酸（Phe）生物合成是一个关键过程，因为 Phe 是蛋白质和苯丙烷类的前体。预苯酸途径将莽草酸（shikimate 途径的最终产物）与 Phe 和酪氨酸的生物合成连接起来。已经报道了两种替代的 Phe 生物合成途径：一种依赖于芳基酸，另一种依赖于苯丙酮酸。虽然芳基酸途径被认为是主要途径，但苯丙酮酸途径的作用仍不清楚。在这里，我们报告说，双功能芳基酸脱水酶（ADT）/预苯酸脱水酶（PDT）酶 ADT2 的缺乏会导致胚胎停滞和种子败育。这一结果明确区分了 ADT2 的必需作用和来自拟南芥的其余 5 个 ADT 基因的作用，这些基因的功能大多重叠。我们发现，来自酵母的单功能 PDT PHA2 在定位于质体时可以恢复 adt2 表型，但在细胞质中表达时则不能。表达单功能 ADT ADT3 也可以得到类似的结果。这些结果表明，当在种子形成过程中，双功能 ADT2 被其他 ADT 或 PDT 酶取代时，可以从苯丙酮酸或芳基酸合成 Phe，这突出了 Phe 生物合成对胚胎发育的重要性，并为 Phe 生物合成的可塑性提供了进一步的见解。
