丛枝菌根真菌对适度干旱诱导甘草酸合成的影响机制研究

Arbuscular mycorrhizal (AM) fungi are widespread soil microorganisms able to establish a symbiotic association with the roots of most terrestrial plants. AM plants have an improved ability for nutrient uptake and tolerance to biotic and abiotic stresses. Many previous studies proved the positive effects of AM on plant drought tolerance and accumulation of secondary metabolites with pharmacological characteristics. This mutualistic symbiosis has great applications in cultivation of medicinal plants for obtaining a high level of glycyrrhizic acid (GA), the synthesis of which can also be induced by moderate drought stress. However, experimental evidences are still lacking to support the pathways of hydraulic signals and chemical signals in AM fungal effects on moderate drought stress induced GA synthesis. In the proposed project, two-compartment cultivation system incorporating an air-gap device will be used to characterize the direct effect of AM effects on water uptake. Meanwhile, vertical two-compartment experiment will be established to analyze the long term effects of AM fungi on hydraulic redistribution. Based on data of key genes expression of GA synthesis pathway and GA concentration, the direct and indirect involvement of AM effects related to hydraulic signals will be investigated. Furthermore, the consequences of AM effects through the chemical signals due to the blockage of the abscisic acid (ABA) pathway with application of ABA synthesis inhibitors will be studied under hydroponic conditions. Chemical signals related genes will be identified by applying RNA-Seq technology, and potential signal pathways will be explored. By split-root experiment, the synergy effects of AM fungi and moderate drought stress in regulation GA synthesis will be uncovered. Therefore, the present study is expected to elucidate the effect of AM symbiosis in plant secondary metabolism, and more importantly to reveal the underlying pathways. The study will also lay foundations for further research into the AM fungi application in medicinal plants cultivation.

丛枝菌根（AM）真菌作为连接植物和土壤的关键因子，在调节植物水分生理和次生代谢产物合成中具有重要作用，显著影响适度土壤干旱诱导甘草酸合成，其通过水分信号及化学信号途径的调节过程是揭示AM真菌作用机制重要的突破口。本项目拟利用空气隔板隔网分室和垂向分室植物培养装置，通过水分荧光标记和甘草酸合成途径关键基因表达分析，研究AM真菌直接和间接调节水分信号的作用机制；在水培条件下施用ABA合成抑制剂研究AM真菌介导ABA途径的调节模式，结合RNA-Seq技术挖掘潜在的化学信号通路，利用分根装置研究AM真菌和适度干旱胁迫调控甘草酸合成的协同作用机制。通过本项目的实施，将能够较为全面的揭示AM真菌影响植物次生代谢的作用机制和潜在的调控途径，并期望推动AM真菌生态生理基础研究和应用技术的发展。

针对目前药用植物甘草栽培中存在的产量与质量问题，本项目利用丛枝菌根（AM）真菌这一连接植物和土壤的关键因子，结合水分调节植物次生代谢的理论假说，探索AM真菌和水分交互作用在促进甘草药用成份积累中的效应及其机制。本项目通过盆栽试验设置水分梯度，分析了AM真菌对甘草生长及次生代谢产物甘草酸含量的影响，结果表明适度干旱胁迫条件下AM真菌接种可以改善甘草生长，并促进根系甘草酸的积累，并证实了AM真菌能够通过促进植物磷的吸收，调节碳氮比及甘草酸生物合成途径关键基因表达等机制调节甘草酸积累；通过转录组和代谢组分析了适度干旱胁迫条件下AM真菌接种对甘草生长及次生代谢的影响，揭示了AM真菌接种能够调控植物激素和信号转导相关基因的表达，影响甘草植株生长及对干旱胁迫的抗性，进而影响次生代谢物的积累。本项目研究了AM真菌介导磷吸收在提高甘草根系甘草酸积累中的作用机制，结果表明，当接种和对照植株具有相似的磷含量时，二者也具有相似的甘草酸含量及相似的生物合成途径关键基因表达量，证实了AM真菌接种改善植物磷营养状况在促进甘草酸含量积累中具有重要作用；利用13C-同位素脉冲标记技术，从碳分配角度探究了AM真菌接种调控物质分配进而影响甘草次生代谢的机理，证实了AM真菌接种可以通过调控植株碳在地上部及根系间，以及在根系各类代谢物间的分配从而影响植物次生代谢，同时这个过程依赖于土壤磷的有效性及菌根侵染程度。本研究设置了在灭菌和非灭菌土壤中接种和不接种AM真菌的处理，证实了AM真菌可以补偿土著微生物群落的缺失，维持甘草正常生长和次生代谢产物积累；还通过甘草大田原位栽培试验，研究了AM真菌接种对大田栽培甘草生长及根系甘草酸含量长期积累效应。综上，本项目通过系列试验较为系统的探究了AM真菌接种促进药用植物甘草生长及次生代谢物积累的机制和潜在的调控途径，为AM真菌在药用植物栽培中的应用奠定了理论和实践基础。