AMF介导的细胞壁“库”积累在提高滇杨Cd耐性中的作用机制研究

Populus yunnanensis, as a major pioneer tree species of ecological and economic importance, showed a great adaptation to the extreme edaphic conditions of Yunnan metalliferous mine tailings, where the soil not only contains the high concentrations of heavy metals, but also the generally low contents of organic matter and nutrients as well as the low water retention capacity. More prevailing evidence reveals that arbuscular mycorrhizal (AM) fungi significantly enhance their host plants’ tolerance against heavy metal stress, and contribute to ecological rehabilitation on vegetation recruitment. Especially, it is true for Populus yunnanensis, relevant for phytomanaging trace element for the purposes both for timber production and phytoremediation, which benefits from the bioaugmentation by AM fungi to survive on extremely contaminated lands. However, the tolerance and alleviation mechanisms involved with AM fungi have not yet been elucidated. In the current application, we will study mechanisms and vital roles for the cell wall bioaccumulation in the enhanced cadmium tolerance of P. yunnanensis bioaugmented by AM fungi, to comparatively analyze the altering subcellular distribution and chemical forms of cadmium in AMF-inoculated P. yunnanensis and the improved resistance against cadmium toxicity, in contrast to non-inoculated poplar, using the combination with transmission electron microscopy, X-ray absorption spectroscopy, and physiological and molecular methods. Meantime, we will also study the physiological, cytological and molecular mechanisms of the enhanced Cd accumulation in cell-wall components of AMF-inoculated P. yunnanensis, by exploring the modified characteristics of cell wall components such as pectin, hemicellulose, and their shifted functional groups, mainly involved in Cd chelation, such as hydroxyl, amine, amide, using the methods in enzymology, RNA-seq, and ecotoxicology. Compared with the non-inoculated controls, the functional roles of cell wall remodeling by AM fungi is to be evaluated in the bioaugmented tolerance of P. yunnanensis against cadmium. The implementation of this application is to strengthen our knowledge on the management of AM fungi to enhance phytoremediation and to provide a theoretical basis and technical support for the use of AM fungi-plant joint phytoremediation of heavy metal mine contaminated soil.

作为重要的经济和生态树种，滇杨在云南矿区显示出优良的“适地”性能，而菌根的形成显著增强滇杨的重金属耐性和“适地”性，但作用机制尚不清楚。本研究以滇杨根、叶细胞壁对丛枝菌根真菌（AMF）定殖的响应为切入点，1）拟利用电镜、X-射线能谱联用技术对实验接种组和对照组植物体内镉分布进行原位表征，探讨细胞壁固持在AMF提高滇杨镉耐性中的作用；2）比较分析AMF对滇杨细胞壁各组分及镉吸附配位官能团分布的影响，阐明AMF强化滇杨细胞壁镉积累的生态生理基础；3）以细胞壁代谢关键酶为对象，探讨AMF强化滇杨细胞壁Cd积累的酶学基础；4）并从RNA水平上探讨AMF强化滇杨细胞壁镉积累的分子机制。通过数据集成、对比分析，从“菌-根”共生关系视角，探讨AMF介导的细胞壁“库”积累镉在强化宿主耐性中的作用及机制，为利用菌根技术促进滇杨在裸露矿区土壤人工恢复、重建和矿区土壤的菌根-植物联合修复提供理论依据和技术支撑。

菌根真菌（Mycorrhizal Fungus）是矿区植物根系的一个重要组成部分，其在植物适应矿区胁迫土壤中的功能作用及机制尚缺乏系统性研究。我们的研究发现，与不接种对照相比，菌根菌接种显著上调参与植物细胞壁合成相关通路基因的表达、调控，激活了宿主植物细胞壁合成关键酶活性，进一步改变细胞壁组分和镉吸附配位官能团的分布，强化了细胞壁对被根系所吸收游离镉离子的固持与区室化解毒作用，进而改变镉离子在宿主植物根系组织、细胞和亚细胞水平上的分布，从而限制其向细胞原生质体和地上部分的运输，由此减轻Cd对宿主植物细胞的毒害，提高植物在矿区土壤中的“适应性”。同时，菌根菌还可以通过强化根际土壤对毒性重金属离子的螯合，显著降低DTPA可提取态镉浓度，减少根系镉吸收和地上部的积累；NMT结果进一步表明AMF接种可通过抑制滇杨根细胞Ca2+通道蛋白活性和H+泵作用，抑制滇杨镉离子的跨膜转运、吸收；还进一步影响根系对Mg、Cu和K等营养元素的积累、再分配，有助于滇杨金属营养元素的稳态；同时，菌根菌接种还通过提高滇杨抗氧化系统活性，缓解毒性Cd离子造成的过氧化胁迫；强化对植物体内富集重金属的螯合，转化成低毒态；RNA-seq结果则进一步证实了AMF接种参与重金属代谢响应的全部9个相关基因丛（Gene clusters）的表达和调控过程，是一个系统性的响应和调控过程。结果表明，菌根菌提高宿主重金属抗性亦是宿主植物延展性表型的一个组成部分。研究结果为利用菌根技术促进滇杨复垦矿区废弃地提供理论支持和技术支撑。