GDP-d-mannose 3,5-epimerase (GME) plays a key role at the intersection of ascorbate and non-cellulosic cell-wall biosynthesis in tomato
GDP-d-mannose 3,5-epimerase (GME) plays a key role at the intersection of ascorbate and non-cellulosic cell-wall biosynthesis in tomato
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DOI：
10.1111/j.1365-313x.2009.03972.x
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发表时间：
2009-11-01
期刊：
影响因子：
7.2
通讯作者：
Baldet, Pierre
中科院分区：
文献类型：
--
作者：
Gilbert, Louise;Alhagdow, Moftah;Baldet, Pierre
P> GDP-d-甘露糖3，5-差向异构酶（GME，EC 5.1.3.18）将GDP-d-甘露糖转化为GDP-l-半乳糖，通常被认为是高等植物中主要抗坏血酸生物合成途径的中心酶，但缺乏其在植物中作用的实验证据。使用转基因番茄品系的RNAi沉默的GME，我们证实，GME确实发挥了关键作用，在调节植物中的抗坏血酸生物合成。此外，转基因番茄品系表现出影响细胞分裂和细胞扩增的生长缺陷。转基因植物的另一个显著特征是它们的脆弱性和果实硬度的损失。叶片和发育中的果实的细胞壁组成的分析表明，细胞壁单糖含量在转基因株系中发生了改变，特别是那些直接与GME活性相关的单糖，如甘露糖和半乳糖。与此一致，免疫细胞化学分析表明，增加甘露聚糖标记在茎和果壁和鼠李糖半乳糖醛酸标记在茎单独。细胞壁甘露聚糖酶裂解产物的MALDI-TOF指纹分析结果表明，在转基因株系中合成了具有乙酸酯取代度的特定甘露聚糖结构。当考虑在一起，这些研究结果表明，在植物中的抗坏血酸和非纤维素细胞壁多糖的生物合成之间的紧密联系，这一事实有助于解释在看似无关的性状，如水果硬度和抗坏血酸含量的共同因素。
P>The GDP-d-mannose 3,5-epimerase (GME, EC 5.1.3.18), which converts GDP-d-mannose to GDP-l-galactose, is generally considered to be a central enzyme of the major ascorbate biosynthesis pathway in higher plants, but experimental evidence for its role in planta is lacking. Using transgenic tomato lines that were RNAi-silenced for GME, we confirmed that GME does indeed play a key role in the regulation of ascorbate biosynthesis in plants. In addition, the transgenic tomato lines exhibited growth defects affecting both cell division and cell expansion. A further remarkable feature of the transgenic plants was their fragility and loss of fruit firmness. Analysis of the cell-wall composition of leaves and developing fruit revealed that the cell-wall monosaccharide content was altered in the transgenic lines, especially those directly linked to GME activity, such as mannose and galactose. In agreement with this, immunocytochemical analyses showed an increase of mannan labelling in stem and fruit walls and of rhamnogalacturonan labelling in the stem alone. The results of MALDI-TOF fingerprinting of mannanase cleavage products of the cell wall suggested synthesis of specific mannan structures with modified degrees of substitution by acetate in the transgenic lines. When considered together, these findings indicate an intimate linkage between ascorbate and non-cellulosic cell-wall polysaccharide biosynthesis in plants, a fact that helps to explain the common factors in seemingly unrelated traits such as fruit firmness and ascorbate content.