Carbon availability triggers fungal nitrogen uptake and transport in arbuscular mycorrhizal symbiosis
Carbon availability triggers fungal nitrogen uptake and transport in arbuscular mycorrhizal symbiosis
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DOI：
10.1073/pnas.1118650109
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发表时间：
2012-02-14
影响因子：
11.1
通讯作者：
Buecking, Heike
中科院分区：
文献类型：
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作者：
Fellbaum, Carl R.;Gachomo, Emma W.;Buecking, Heike
丛枝菌根（AM）共生是大多数陆地植物与普遍存在的肾小球菌门（Glomeromycota）土壤真菌之间形成的共生关系，负责大量的养分转移和全球碳固存。AM真菌从土壤中吸收养分，并与寄主的光合作用固定碳(C)进行交换。最近的研究表明，植物和真菌伙伴的互惠奖励策略保证了伙伴之间磷与C的“公平交易”[Kiers ET, ET al. (2011) Science 333: 880-882]，但是否有类似的奖励机制也控制着AM共生中的氮(N)通量尚不清楚。利用菌根器官培养技术，研究了AM共生中对氮源的吸收和运输、精氨酸酶和脲酶的酶活性以及根外和根内菌丝体中真菌基因的表达。我们发现寄主植物的C供应触发了共生中N的吸收和运输，并且N运输的增加是由真菌基因表达的变化协调的。共生关系中的N运输仅在C由宿主通过菌根界面输送时才会受到刺激，而当C以醋酸盐的形式直接供给真菌根外菌丝体时则不会。这些发现支持了从根部到真菌的碳通量作为氮吸收和运输的关键触发因素的重要性，并为AM共生中的氮运输调节提供了见解。
The arbuscular mycorrhizal (AM) symbiosis, formed between the majority of land plants and ubiquitous soil fungi of the phylum Glomeromycota, is responsible for massive nutrient transfer and global carbon sequestration. AM fungi take up nutrients from the soil and exchange them against photosynthetically fixed carbon (C) from the host. Recent studies have demonstrated that reciprocal reward strategies by plant and fungal partners guarantee a "fair trade" of phosphorus against C between partners [Kiers ET, et al. (2011) Science 333: 880-882], but whether a similar reward mechanism also controls nitrogen (N) flux in the AM symbiosis is not known. Using mycorrhizal root organ cultures, we manipulated the C supply to the host and fungus and followed the uptake and transport of N sources in the AM symbiosis, the enzymatic activities of arginase and urease, and fungal gene expression in the extraradical and intraradical mycelium. We found that the C supply of the host plant triggers the uptake and transport of N in the symbiosis, and that the increase in N transport is orchestrated by changes in fungal gene expression. N transport in the symbiosis is stimulated only when the C is delivered by the host across the mycorrhizal interface, not when C is supplied directly to the fungal extraradical mycelium in the form of acetate. These findings support the importance of C flux from the root to the fungus as a key trigger for N uptake and transport and provide insight into the N transport regulation in the AM symbiosis.