Tzin Vered, Malitsky Sergey, Aharoni Asaph, Galili Gad
Department of Plant Sciences, The Weizmann Institute of Science, Rehovot 76100, Israel.
Plant J. 2009 Oct;60(1):156-67. doi: 10.1111/j.1365-313X.2009.03945.x. Epub 2009 Jun 6.
Plants can synthesize the aromatic amino acid Phe via arogenate, but it is still not known whether they also use an alternative route for Phe biosynthesis via phenylpyruvate, like many micro-organisms. To examine this possibility, we expressed a bacterial bi-functional PheA (chorismate mutase/prephenate dehydratase) gene in Arabidopsis thaliana that converts chorismate via prephenate into phenylpyruvate. The PheA-expressing plants showed a large increase in the level of Phe, implying that they can convert phenylpyruvate into Phe. In addition, PheA expression rendered the plants more sensitive than wild-type plants to the Trp biosynthesis inhibitor 5-methyl-Trp, implying that Phe biosynthesis competes with Trp biosynthesis from their common precursor chorismate. Surprisingly, GC-MS, LC-MS and microarray analyses showed that this increase in Phe accumulation only had a very minor effect on the levels of other primary metabolites as well as on the transcriptome profile, implying little regulatory cross-interaction between the aromatic amino acid biosynthesis network and the bulk of the Arabidopsis transcriptome and primary metabolism. However, the levels of a number of secondary metabolites derived from all three aromatic amino acids (Phe, Trp and Tyr) were altered in the PheA plants, implying regulatory cross-interactions between the flux of aromatic amino acid biosynthesis from chorismate and their further metabolism into various secondary metabolites. Taken together, our results provide insights into the regulatory mechanisms of aromatic amino acid biosynthesis and their interaction with central primary metabolism, as well as the regulatory interface between primary and secondary metabolism.
植物可以通过预苯酸合成芳香族氨基酸苯丙氨酸，但它们是否也像许多微生物一样利用经由苯丙酮酸的另一条苯丙氨酸生物合成途径尚不清楚。为了研究这种可能性，我们在拟南芥中表达了一个细菌双功能苯丙氨酸转氨酶（分支酸变位酶/预苯酸脱水酶）基因，该基因可将分支酸通过预苯酸转化为苯丙酮酸。表达苯丙氨酸转氨酶的植物中苯丙氨酸水平大幅增加，这意味着它们可以将苯丙酮酸转化为苯丙氨酸。此外，苯丙氨酸转氨酶的表达使这些植物比野生型植物对色氨酸生物合成抑制剂5-甲基色氨酸更敏感，这意味着苯丙氨酸生物合成与从它们的共同前体分支酸开始的色氨酸生物合成相互竞争。令人惊讶的是，气相色谱-质谱联用（GC-MS）、液相色谱-质谱联用（LC-MS）和微阵列分析表明，苯丙氨酸积累的这种增加对其他初级代谢产物的水平以及转录组图谱只有非常微小的影响，这意味着芳香族氨基酸生物合成网络与拟南芥转录组和初级代谢的大部分之间几乎没有调节性交叉相互作用。然而，在表达苯丙氨酸转氨酶的植物中，源自所有三种芳香族氨基酸（苯丙氨酸、色氨酸和酪氨酸）的许多次生代谢产物的水平发生了变化，这意味着从分支酸开始的芳香族氨基酸生物合成通量与其进一步代谢为各种次生代谢产物之间存在调节性交叉相互作用。综上所述，我们的结果为芳香族氨基酸生物合成的调节机制及其与中心初级代谢的相互作用，以及初级和次级代谢之间的调节界面提供了见解。
