丛枝菌根对植物适应干旱胁迫的生态重要性及其生理机制研究

Arbuscular mycorrhiza (AM), a ubiquitous symbiotic association established between AM fungi and roots of higher plants in most terrestrial ecosystems, is essentially important for plant adaptation to various environmental stresses, such as nutrient deficiency, environmental pollution and drought, etc. Many studies have proved the positive influences of AM on plant drought tolerance and made efforts to uncover the underlying mechanisms. However, experimental evidences are still lacking to support the ecological significance of AM associations in natural ecosystems suffering water shortage, and available information is so far very limited as for the molecular mechanisms underlying the enhanced plant drought tolerance by AM symbiosis. In the proposed project, Northeast China Transect that covers different grassland ecosystems ranging from meadow steppe to desert steppe is selected as target research area to reveal synergetic succession of plant and AM fungal communities along the natural precipitation gradients.The effects of drought stress on physiological function of the mycorrhizal symbiosis, which is characterized by carbon-phosphorus exchange between AM fungi and host plants, will be examined based on controlled-environment experiment. Furthermore, split-root cultivation experiment will be performed with ABA defective plant mutant as experimental materials to understand the regulation mechanism of plant physiological responses to drought stress by AM fungi. Drought tolerance related genes from AM fungi themselves will be explored by using suppression subtractive hybridization techniques, and consequently the signaling pathway between AM fungi and host plants will be investigated. The study is expected to demonstrate the ecological significance of AM symbiosis in plant drought tolerance, and more importantly to reveal the underlying molecular mechanisms. It will also lay foundations for further research into the synergetic stress resistance of AM symbiosis.

很多研究证实丛枝菌根（AM）对植物适应干旱胁迫具有重要积极作用，但在水分受限的自然生态系统中，对于菌根共生体系的生态重要性还缺少试验证据。至于AM增强植物抗旱性的分子机制，尤其是干旱胁迫下共生体系的逆境信号交流途径和协同响应机制，相关基础研究更显薄弱。本项目以我国东北样带为研究平台，通过系统的生态调查解析植物群落和AM真菌生物多样性随降水梯度的变化规律，同时以菌根真菌和宿主植物之间的碳磷交换强度指示其相互依存程度，通过控制环境生物学试验揭示共生体系生理机能和干旱胁迫程度之间的关系。另一方面，结合植物ABA缺陷型突变体和分根培养试验探讨AM真菌对植物干旱胁迫响应的分子调控机制；应用抑制消减杂交技术探寻AM真菌抗旱相关基因，进而探讨干旱胁迫下AM真菌与宿主植物的信号交流和协同抗逆机制。预期本项目的实施能够系统揭示AM对植物适应干旱胁迫的生态重要性及其生理机制，并为后续深入研究奠定基础。

丛枝菌根真菌（arbuscular mycorrhizal fungi, AMF）能与绝大多数陆地高等植物形成菌根共生体系，对于植物适应各种生物与非生物胁迫有重要积极作用，但目前对于AM真菌在植物适应干旱胁迫中的生态重要性及其生理机制还缺乏系统深入研究。本项目在以降水为主要环境梯度的中国东北样带开展野外调查，发现AM真菌在研究区域内不同草原生态系统均具有较高的多样性，AM真菌群落结构受到年均温、年均降雨量和土壤性质的显著影响。在我国北方农牧交错带的调查研究则表明AM真菌群落对降水表现出强依赖性，而不同AM真菌类群对气候变量的反应存在显著差异。长期定位实验进一步证实增雨降低了AM真菌生物量，显著改变了AM真菌群落结构。另一方面，我们通过模拟生物学实验深入探讨了AM真菌与植物协同抗旱的分子机制，揭示了AM真菌能够通过调节植物ABA信号途径中的关键功能基因，如14-3-3蛋白基因，水孔蛋白基因等增强植物抗旱性。分根培养试验表明干旱胁迫下AM真菌显著诱导植物中编码肌醇-3-磷酸合酶（IPS）和14-3-3蛋白基因的表达，从而导致植物水孔蛋白基因表达的增强，改善了植物水分状况。进一步数据分析显示，IPS和14-3-3蛋白可能作为正调节子启动共生体系信号交流和协同抗旱机制。通过转录组和代谢组分析，证明干旱胁迫条件下AM真菌通过调控植物类苯基丙烷的合成代谢途径，促进木质素的合成和运输，增强细胞壁的强度。同时，AM通过上调植物糖酵解代谢途径中的关键基因，促进植物糖类物质的分解和脂肪酸的代谢，提高植物耐旱性，而AM真菌可以提高糖酵解代谢和P450代谢过程增强自身抗逆性。综上，本项目通过样带调查和野外定位试验揭示了包括降水在内的环境因子对AM真菌多样性和群落结构的影响，同时通过模拟生物学试验探讨了AM真菌与植物协同抗旱的分子机制，从而较为全面地揭示了AM共生体系对植物适应干旱胁迫的生态重要性及其生理机制，为后续深入研究奠定了基础。