The Functions of Chloroplast Glutamyl-tRNA in Translation and Tetrapyrrole Biosynthesis1[OPEN]
The Functions of Chloroplast Glutamyl-tRNA in Translation and Tetrapyrrole Biosynthesis1[OPEN]
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DOI：
10.1104/pp.20.00009
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发表时间：
2020-05-01
期刊：
影响因子：
7.4
通讯作者：
Bock, Ralph
中科院分区：
文献类型：
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作者：
Agrawal, Shreya;Karcher, Daniel;Bock, Ralph
转质体烟草的产生和鉴定为叶绿体谷氨酰-tRNA在蛋白质合成和四吡咯合成中的双重作用提供了新的认识。除了在翻译中起作用外，它还作为谷氨酰-tRNA还原酶（GluTR）的底物，该酶催化四吡咯生物合成途径中的关键步骤。tRNA（Glu）库如何在两个途径之间分布以及tRNA（Glu）分配是否限制四吡咯生物合成和/或蛋白质生物合成仍然知之甚少。我们产生了一系列的transplastomic烟草（烟草）植物改变tRNA（Glu）的表达水平，并引入了点突变到质体trnE基因，据报道，解偶联蛋白质的生物合成从四吡咯生物合成的叶绿体中的原生生物Euglena gracilis。我们表明，而不是可比的解偶联的两个途径，trnE突变是致命的烟草，因为它抑制tRNA加工，从而防止翻译的Glu密码子。突变的trnE基因的异位表达揭示了未成熟的tRNA（Glu）对谷氨酰-tRNA还原酶的意想不到的抑制。我们进一步证明，而过量表达的tRNA（Glu）不影响四吡咯的生物合成，减少GluTR活性通过抑制tRNA（Glu）前体导致四吡咯合成成为限制在早期植物发育时，积极的光系统生物合成挑起高需求从头叶绿素生物合成。总而言之，我们的研究结果提供了对tRNA（Glu）在蛋白质生物合成和四吡咯生物合成交叉点中的作用的深入了解。
The generation and characterization of transplastomic tobacco plants provide insight into the dual role of the chloroplast glutamyl-tRNA in protein biosynthesis and tetrapyrrole biosynthesis.The chloroplast glutamyl-tRNA (tRNA(Glu)) is unique in that it has two entirely different functions. In addition to acting in translation, it serves as the substrate of glutamyl-tRNA reductase (GluTR), the enzyme catalyzing the committed step in the tetrapyrrole biosynthetic pathway. How the tRNA(Glu) pool is distributed between the two pathways and whether tRNA(Glu) allocation limits tetrapyrrole biosynthesis and/or protein biosynthesis remains poorly understood. We generated a series of transplastomic tobacco (Nicotiana tabacum) plants to alter tRNA(Glu) expression levels and introduced a point mutation into the plastid trnE gene, which has been reported to uncouple protein biosynthesis from tetrapyrrole biosynthesis in chloroplasts of the protist Euglena gracilis. We show that, rather than comparable uncoupling of the two pathways, the trnE mutation is lethal in tobacco because it inhibits tRNA processing, thus preventing translation of Glu codons. Ectopic expression of the mutated trnE gene uncovered an unexpected inhibition of glutamyl-tRNA reductase by immature tRNA(Glu). We further demonstrate that whereas overexpression of tRNA(Glu) does not affect tetrapyrrole biosynthesis, reduction of GluTR activity through inhibition by tRNA(Glu) precursors causes tetrapyrrole synthesis to become limiting in early plant development when active photosystem biogenesis provokes a high demand for de novo chlorophyll biosynthesis. Taken together, our findings provide insight into the roles of tRNA(Glu) at the intersection of protein biosynthesis and tetrapyrrole biosynthesis.