Carbon export from arbuscular mycorrhizal roots involves the translocation of carbohydrate as well as lipid
Carbon export from arbuscular mycorrhizal roots involves the translocation of carbohydrate as well as lipid
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DOI：
10.1104/pp.102.007765
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发表时间：
2003-03-01
期刊：
影响因子：
7.4
通讯作者：
Shachar-Hill, Y
中科院分区：
文献类型：
--
作者：
Bago, B;Pfeffer, PE;Shachar-Hill, Y
丛枝菌根(AM)真菌从植物根部吸收光合作用固定的碳，并将其运输到外部菌丝体。此前的实验表明，根部碳水化合物合成的真菌脂是输出碳的一种形式。在这项研究中，对C-13(1)葡萄糖提供给AM根后储存的碳水化合物和结构碳水化合物的标记分析表明，这并不是碳从茎内流向茎外菌丝体(ERM)的唯一途径。在共生发展过程中，糖原、甲壳素和海藻糖的标记模式与大量输出的糖原是一致的。在表达的基因中，鉴定了糖原合成酶、糖原分支酶、甲壳素合成酶以及甲壳素合成的第一酶(谷氨酰胺果糖-6-磷酸转氨酶)的推测序列。菌根、萌发孢子和ERM中糖原合成酶基因表达的定量结果与C-13标记的乙酸酯和甘油的标记观察结果一致，两者都表明糖原是由真菌在萌发孢子和共生过程中合成的。讨论了标记分析和基因序列对调节碳水化合物代谢的意义，并提出了糖原在AM共生中的4倍作用：从寄主获取的己糖的隔离，在孢子中的长期储存，从茎内菌丝体到ERM的转位，以及整个生命周期细胞内己糖水平的缓冲。
Arbuscular mycorrhizal (AM) fungi take up photosynthetically fixed carbon from plant roots and translocate it to their external mycelium. Previous experiments have shown that fungal lipid synthesized from carbohydrate in the root is one form of exported carbon. In this study, an analysis of the labeling in storage and structural carbohydrates after C-13(1) glucose was provided to AM roots shows that this is not the only pathway for the flow of carbon from the intraradical to the extraradical mycelium (ERM). Labeling patterns in glycogen, chitin, and trehalose during the development of the symbiosis are consistent with a significant flux of exported glycogen. The identification, among expressed genes, of putative sequences for glycogen synthase, glycogen branching enzyme, chitin synthase, and for the first enzyme in chitin synthesis (glutamine fructose-6-phosphate aminotransferase) is reported. The results of quantifying glycogen synthase gene expression within mycorrhizal roots, germinating spores, and ERM are consistent with labeling observations using C-13-labeled acetate and glycerol, both of which indicate that glycogen is synthesized by the fungus in germinating spores and during symbiosis. Implications of the labeling analyses and gene sequences for the regulation of carbohydrate metabolism are discussed, and a 4-fold role for glycogen in the AM symbiosis is proposed: sequestration of hexose taken from the host, long-term storage in spores, translocation from intraradical mycelium to ERM, and buffering of intracellular hexose levels throughout the life cycle.