John Innes Centre, NR4 7UH Norwich, United Kingdom;
School of Natural and Environmental Sciences, Newcastle University, NE1 7RU Newcastle-upon-Tyne, United Kingdom.
Proc Natl Acad Sci U S A. 2019 Jul 23;116(30):15297-15306. doi: 10.1073/pnas.1908556116. Epub 2019 Jul 11.
Large numbers of genes essential for embryogenesis in encode enzymes of plastidial metabolism. Disruption of many of these genes results in embryo arrest at the globular stage of development. However, the cause of lethality is obscure. We examined the role of the plastidial oxidative pentose phosphate pathway (OPPP) in embryo development. In nonphotosynthetic plastids the OPPP produces reductant and metabolic intermediates for central biosynthetic processes. Embryos with defects in various steps in the oxidative part of the OPPP had cell division defects and arrested at the globular stage, revealing an absolute requirement for the production via these steps of ribulose-5-phosphate. In the nonoxidative part of the OPPP, ribulose-5-phosphate is converted to ribose-5-phosphate (R5P)-required for purine nucleotide and histidine synthesis-and subsequently to erythrose-4-phosphate, which is required for synthesis of aromatic amino acids. We show that embryo development through the globular stage specifically requires synthesis of R5P rather than erythrose-4-phosphate. Either a failure to convert ribulose-5-phosphate to R5P or a block in purine nucleotide biosynthesis beyond R5P perturbs normal patterning of the embryo, disrupts endosperm development, and causes early developmental arrest. We suggest that seed abortion in mutants unable to synthesize R5P via the oxidative part of the OPPP stems from a lack of substrate for synthesis of purine nucleotides, and hence nucleic acids. Our results show that the plastidial OPPP is essential for normal developmental progression as well as for growth in the embryo.
大量在胚胎发生中必不可少的基因编码质体代谢的酶。这些基因中的许多破坏会导致胚胎在发育的球形阶段停滞。然而，致死的原因尚不清楚。我们研究了质体氧化戊糖磷酸途径（OPPP）在胚胎发育中的作用。在非光合质体中，OPPP 产生还原物和代谢中间产物，用于中心生物合成过程。在 OPPP 氧化部分的各个步骤中存在缺陷的胚胎具有细胞分裂缺陷，并在球形阶段停滞，这表明通过这些步骤产生核酮糖 5-磷酸是绝对必要的。在 OPPP 的非氧化部分，核酮糖 5-磷酸转化为核糖 5-磷酸（R5P） - 需要嘌呤核苷酸和组氨酸合成 - 随后转化为赤藓糖 4-磷酸，这是合成芳香族氨基酸所必需的。我们表明，通过球形阶段的胚胎发育特别需要 R5P 的合成，而不是赤藓糖 4-磷酸的合成。要么无法将核酮糖 5-磷酸转化为 R5P，要么在 R5P 之后嘌呤核苷酸生物合成受阻，都会扰乱胚胎的正常模式形成，破坏胚乳发育，并导致早期发育停滞。我们认为，无法通过 OPPP 的氧化部分合成 R5P 的突变体中的种子流产源于缺乏嘌呤核苷酸合成的底物，因此缺乏核酸。我们的结果表明，质体 OPPP 对于正常发育进展以及胚胎生长都是必不可少的。
