丛枝菌根形成过程及其信号转导途径

Signal Recognition and Transduction in the Arbuscular Mycorrhizal Symbiosis

丛枝菌根是由一类土壤中古老的丛枝菌根真菌与植物根系形成的互利互惠共生体。通过共生作用丛枝菌根真菌帮助宿主植物提高水和矿质营养(特别是磷)的吸收效率。作为回报,大约20%的光合作用产物被转移到丛枝菌根真菌中,供其完成自身的生活史。丛枝菌根形成的过程中,需要植物与丛枝菌根真菌之间进行一系列信号分子的识别、交换以及信号转导作用,这一过程由一系列植物和菌根真菌的基因控制。首先,植物会分泌一种植物激素——独角金内酯来诱导菌根真菌加速分支,而菌根真菌也会分泌脂质几丁寡糖促进植物与其形成菌根。加速分支的菌根真菌接触到植物根部以后,会附着在植物根的表皮并形成附着胞,通过附着胞穿透植物根的表皮,最后进入维管组织附近的皮层细胞并在其中不断进行二叉分支,形成特有的丛枝结构。通过对模式植物共生现象的研究,已经发现很多植物基因参与到共生形成的信号转导过程中,包括早期植物反应的基因、菌根与根瘤共生共同需要的转导因子以及菌根特异的信号分子等。本文对菌根的形成过程及信号转导途径进行详细的介绍,为人们深入研究菌根关系提供参考。

The arbuscular mycorrhizal（AM） symbiosis is a mutualistic endosymbiosis formed between plants and members of the ancient AM fungi（Glomeromycota） in the soil.AM fungi improve the supply of water and nutrients to host plants,especially phosphorus and nitrogen.In return,AM fungi obtain about 20%of the photosynthesis products from their plant hosts to complete their lifecycle.The development of symbiosis is accompanied by a series of signalling,recognition and transduction processes controlled by genes from both the plant hosts and the AM fungi.First,a novel class of plant hormones known as strigolactone from plant root exudate promote AM fungi branching.The AM fungi also release the signalling molecule＂myc factor＂,now identified to be the same as＂nod factor＂lipochitooligosaccharides,that stimulate formation of AM in plant species of diverse families.When the accelerated branching AM fungi contact the plant roots,they form a prepenetration apparatus＂appressorium＂at the epidermis.Then the hyphae enter the inner cortical cells,forming dichotomously branched hyphae,called arbuscules.In studies of symbiosis in model plants,several plant genes that are required for symbiosis have been identified,including early plant responsive genes,common symbiosis genes that are required for AM and root nodule,and AM symbiosis-special genes.In this paper,we introduce the development of the AM symbiosis,the signal transduction pathway in detail,and provide references for making use of AM symbiosis in agricultural production.