Unloading phosphate for starch synthesis in cereal grains.
Unloading phosphate for starch synthesis in cereal grains.
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DOI：
10.1016/j.molp.2021.06.008
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发表时间：
2021-06
期刊：
影响因子：
27.5
通讯作者：
Lei Xu;Keke Yi
中科院分区：
文献类型：
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作者：
Lei Xu;Keke Yi
大量营养元素磷（P）是植物生长所必需的，对作物产量至关重要。它以无机正磷酸盐[PO 4 3 H2O，HPO 4 2 H2O，H2 PO 4 2 H2O（Pi）]的形式被植物根部从土壤中吸收。由于磷很容易与有机质和矿物质阳离子形成不溶性络合物并沉淀，土壤中磷的生物利用度通常很低，常常限制作物生长和最终产量。为了维持作物产量，农业严重依赖于来自不可再生磷酸盐岩的开采的无机磷肥的消耗，这导致了磷短缺和环境问题的问题（Cong等人，2020年）。因此，如何以最少的磷肥投入提高作物产量是植物科学家面临的一个重大挑战。谷类作物吸收的磷中约有60%-85%最终分配到谷物中，其中大部分合成为植酸盐（Raboy，2001）。除了合成植酸外，磷对籽粒灌浆也是必不可少的。由于谷物的主要成分是淀粉，Pi间接或直接参与淀粉的生物合成。间接地，P是许多代谢物和大分子的关键组分，包括淀粉生物合成所需的ATP、核酸和磷脂。Pi还直接参与淀粉生物合成，因为它是葡萄糖-1-P（G-1-P）的生物合成所必需的，葡萄糖-1-P是胚乳中淀粉生物合成的初始底物。G-1-P和ATP通过ADP-葡萄糖焦磷酸化酶（ADP-glucose pyrophosphorylase，AGP 3）转化为ADP-葡萄糖（ADP-Glc）和无机焦磷酸盐（PPi），ADP-葡萄糖焦磷酸化酶是淀粉生物合成的限速步骤。然而，无机焦磷酸酶可以将PPi水解成Pi，这可以抑制AGEs的催化活性（Jeon等人，2010; Zeeman等人，2010年）。已经证明，在水稻胚乳中表达对抑制剂Pi不敏感的工程改造的AGR 2导致增强的淀粉合成和更高的种子重量（Sakulsingharoj等人，2004年）。因此，在灌浆期限制胚乳中的磷水平，可以保证淀粉的正常合成和作物产量。然而，在籽粒灌浆过程中，胚乳中的磷稳态和淀粉合成是如何协调的尚不清楚。
The macronutrient phosphorus (P) is essential for plant growth and of vital importance to crop yield. It is taken up from the soil in the form of inorganic orthophosphate [PO4 3À, HPO4 2À, H2PO4 À (Pi)] by plant roots. As Pi readily forms insoluble complexes and precipitates with organic matter and mineral cations, Pi bioavailability in the soil is usually low and often limits crop growth and final yield. To sustain crop yields, consumption of inorganic P fertilizer derived from mining of non-renewable phosphate rock is heavily relied upon for agriculture, which causes issues of P scarcity and environmental problems (Cong et al., 2020). Therefore, improving crop yields with minimal P fertilizer input is a major challenge for plant scientists.About 60%–85% of the P absorbed by cereal crops is ultimately allocated into the grain, most of which is synthesized into phytate (Raboy, 2001). Beside the synthesis of phytate in grain, P is also essential for grain filling. As the major component of cereal grains is starch, Pi is indirectly or directly involved in starch biosynthesis. Indirectly, P is a critical component of many metabolites and macromolecules, including ATP, nucleic acids, and phospholipids, which are required for starch biosynthesis. Pi also participates in starch biosynthesis directly as it is required for biosynthesis of glucose-1-P (G-1-P), which is the initial substrate for starch biosynthesis in the endosperm. G-1-P and ATP are then converted into ADP-glucose (ADP-Glc), the glucose donor for starch synthesis, and inorganic pyrophosphate (PPi) by ADP-glucose pyrophosphorylase (AGPase), which is a ratelimiting step in starch biosynthesis. However, the inorganic pyrophosphatase can hydrolyze PPi into Pi, which can inhibit the catalytic activity of the AGPase (Jeon et al., 2010; Zeeman et al., 2010). It was demonstrated that expression of an engineered AGPase, which is insensitive to the inhibitor Pi, in rice endosperm resulted in enhanced starch synthesis and higher seed weights (Sakulsingharoj et al., 2004). Therefore, restriction of Pi level in the endosperm during grain filling could ensure proper starch biosynthesis and crop yields. However, quite how Pi homeostasis and starch synthesis is coordinated in the endosperm during grain filling is unknown.