丛枝菌根真菌脂类代谢对共生信号调控的响应和反馈机制

The arbuscular mycorrhiza (AM) is formed between the arbuscular mycorrhizal fungi and terrestrial host plants, and it is one of the most common types of symbiosis in natural ecosystem, playing an important role in energy flow and nutrient cycling in ecosystem. AM fungal lipid is important for energy storage, biomembrane construction, and signal transduction. The response and feedback of AM fungal lipid metabolism to the regulation of symbiotic signaling is the key for uncovering the secret of mycorrhizal symbiosis. In order to clarify the mechanism of AM fungal lipid metabolism in response to the symbiotic signaling regulation, experiments will be carried out using Glomus intraradices fungal spores, in situ Daucus carrot root system, in situ Medicago truncatula whole plant system, as well as Oryza sativa and Glycine max pot cultures. Drought and low temperature stress conditions will be set up, together with other treatments such as symbiotic or non-symbiotic status, addition of strigolactone or not and so on. The main techniques used include stable isotope tracing, real-time quantified PCR, in situ hybridization, and metabolic flux analysis. Based on the results, we can identify the differences of the AM fungal lipid storage and release processes between symbiosis and non-symbiotic status, and reveal the response and feedback of the AM fungal lipid decomposition process to the early signal transduction during the establishment of symbiosis. At the end, we can elucidate the symbiotic relationship between lipid metabolism and the dialogue of both MAPKs signaling cascade systems of symbiotic sides, as well as the adaptive strategy to adversity. Our study can provide the scientific bases for the development of mycorrhizal symbiotic theory and promote the application of AM symbiosis.

丛枝菌根（Arbuscular mycorrhiza, AM）真菌和陆生植物形成的菌根，是自然生态系统中最为普遍存在的共生形式之一，在生态系统物质循环和能量流动中发挥巨大作用。脂类对AM真菌的能量存储、生物膜构成、及信号转导至关重要，而AM真菌脂类代谢对共生信号调控的响应和反馈机制更是揭开菌根共生秘密的关键所在。本项目以AM真菌孢子、胡萝卜原位根系统、蒺藜苜蓿整株原位系统、以及水稻和大豆盆栽系统为材料，设置干旱、低温逆境条件，并结合共生或非共生状态、有无外源添加独脚金内酯等处理，利用稳定同位素示踪、基因实时定量表达、原位杂交、以及代谢通量分析等方法，解析在共生和非共生状态下AM真菌脂类存储和释放过程的本质不同，揭示共生建立初期脂类分解对信号调控的响应和反馈机制，并阐明共生关系维持中脂类代谢与双方MAPKs信号级联系统的耦合机制及其对逆境的适应策略，为发展共生理论、促进菌根应用提供科学依据。

菌根（Mycorrhiza）是菌根真菌和宿主植物形成的共生体，是世界上最为普遍存在的共生形式之一。AM共生体的建立需要宿主植物释放共生信号分子，如独脚金内酯（Strigolactones, SLs），启动和激活宿主植物下游信号的发生。脂类在真菌中扮演着重要的角色，它不仅是生物膜结构的主要构成成分，同时在物质、能量的存储与释放，以及各种分子信号转导中具有重要的作用。因此，对AM真菌脂类代谢过程的解析，特别是与共生体建立初期以及共生关系维持中信号调控之间的相互作用机制，将是解开菌根真菌秘密的关键所在。本项研究结论如下：.对野生和栽培水稻进行AMF接种试验，发现接种AMF的野生和栽培水稻均表现出抗病性增强，并且野生水稻比栽培水稻表现出更强的抗病性；转录组测序结果表明在受到病原菌刺激后，野生和栽培水稻接种AMF均能引起生长素和水杨酸对病原菌的拮抗能力；接种AMF的野生水稻中的茉莉酸途径和甲戊酸酯途径显著富集，而接种AMF的栽培水稻中油菜素类固醇合成相关基因显著富集。对栽培大豆和野生大豆进行AMF接种试验，发现干旱胁迫下接种AMF能刺激野生和栽培大豆根系伸长生长；干旱胁迫下脯氨酸含量、丙二醛含量、过氧化氢酶活性、GintAQPF1和GintAQPF2表达量均显著高于未接种对照组。对人参进行AMF接种试验，结果表明接种AMF能够促进人参侧根伸长，增加人参皂苷含量，同时提高人参根系活力。此外，接种AMF的人参根际细菌群落多样性增加，根际有益细菌的种类增加而根际有害真菌种类减少。最后，对水稻独脚金内酯生物合成通路和根际微生物的耦合分析结果表明，与野生型相比，独脚金内酯突变体d17和d14的根际细菌丰富度指数较高，而真菌的丰富度较低；共相关分析结果表明，调控独脚金内酯相关的代谢基因能够显著影响水稻根际微生物的组成，说明了独脚金内酯生物和信号转导途径在水稻根际微生物组的形成中起到非常重要的作用，为今后独脚金内酯诱导和菌根共生体的研究提供了理论基础。