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拟南芥蔗糖合酶 2 和 3 调节代谢平衡,并将碳直接导向发育种子中的淀粉合成。

Arabidopsis sucrose synthase 2 and 3 modulate metabolic homeostasis and direct carbon towards starch synthesis in developing seeds.

机构信息

Departamento de Ingeniería Genética, CINVESTAV Unidad Irapuato, CP 36821 Irapuato, Guanajuato, México.

出版信息

Planta. 2010 Aug;232(3):701-18. doi: 10.1007/s00425-010-1207-9. Epub 2010 Jun 18.

Abstract

Two genes encoding sucrose synthase (SUS), namely SUS2 (At5g49190) and SUS3 (At4g02280), are strongly and differentially expressed in Arabidopsis seed. Detailed biochemical analysis was carried out in developing seeds 9-21 days after flowering (DAF) of wild type and two knockouts. SUS2 and SUS3 are not redundant genes since single knockouts show a phenotype in developing seeds. The mutants had 30-50% less SUS activity and therefore accumulated 40% more sucrose and 50% less fructose at 15 DAF. This did not affect the hexose-P pool, but led to 30-70% less starch in embryo and seed coat. Lipids were 55% higher in both mutants at 9-15 DAF. It seems that sucrolysis via SUS is not required for oil or protein synthesis but rather for channeling carbon toward ADP-glucose and starch in seeds. Metabolite profiling with GC-TOF revealed specific downstream changes in primary metabolism as a consequence of signaling or regulatory fine-tuning. While sucrose increased, hexoses and specific amino acids decreased reciprocally. There was a developmental shift regarding an earlier timing of dry weight accumulation, germinative maturity, oil deposition, sugar levels, transient starch buildup, and protein storage. Nevertheless, final seed size and composition were unaltered due to an earlier cessation of growth, thus giving rise to an apparent silent phenotype of mature mutant seeds. We conclude that SUS is important for metabolite homeostasis and timing of seed development, and propose that an altered sucrose/hexose ratio can modify carbon partitioning and the pattern of storage compounds in Arabidopsis.

摘要

两个编码蔗糖合酶(SUS)的基因,即 SUS2(At5g49190)和 SUS3(At4g02280),在拟南芥种子中强烈且差异表达。在野生型和两个敲除突变体开花后 9-21 天(DAF)的发育种子中进行了详细的生化分析。SUS2 和 SUS3 不是冗余基因,因为单个敲除突变体在发育种子中表现出表型。突变体的 SUS 活性降低了 30-50%,因此在 15 DAF 时蔗糖积累增加了 40%,果糖减少了 50%。这并没有影响己糖-P 池,但导致胚和种皮中的淀粉减少 30-70%。在 9-15 DAF 时,两个突变体中的脂质含量均增加了 55%。似乎通过 SUS 的蔗糖分解不是油或蛋白质合成所必需的,而是将碳导向种子中的 ADP-葡萄糖和淀粉。GC-TOF 的代谢物分析揭示了初级代谢物中特定的下游变化,这是信号或调节微调的结果。蔗糖增加的同时,己糖和特定氨基酸则相反地减少。在干重积累、萌发成熟度、油脂沉积、糖水平、瞬时淀粉积累和蛋白质储存方面,出现了发育性转变。然而,由于生长较早停止,最终种子大小和组成没有改变,从而导致成熟突变体种子出现明显的沉默表型。我们得出结论,SUS 对代谢物平衡和种子发育的时间至关重要,并提出改变蔗糖/己糖比可以改变碳分配和拟南芥中储存化合物的模式。

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