林木共生菌系统及其作用机制——以杨树为例

杨树（Populus）是重要造林树种,也是研究林木基础生物学性状的模式材料。不仅如此,杨树可与多种细菌（内生细菌、内生固氮菌和根际促生菌）和真菌（外生菌根真菌、丛枝菌根真菌和内生真菌）类群建立共生关系,为揭示树木和微生物之间的互惠共生机制提供了理想模型。这些共生菌能积极调控林木生长发育、营养吸收和生理生态过程。目前在杨树-双色蜡蘑（Laccaria bicolor）形成的外生菌根发育、提高杨树耐盐、耐重金属的生理与分子机制、叶片内生真菌群落结构与病害发生、菌根辅助细菌和菌丝内共生细菌-真菌-杨树形成的三重跨界共生等方面取得多项突破。近年来,一批模式草本植物微生物组（microbiome）计划相继实施,对共生菌群落结构和功能的认识有了革命性的进步。以美洲黑杨、毛果杨和胶杨为代表的林木微生物组研究也已启动,表明宿主基因型和环境因子可显著影响共生菌群落结构与物种组成;在根际（rhizosphere）和内生（endosphere）环境存在结构和功能迥异的菌群。另一方面,以根系为诱饵,通过宿主表型来推测菌群功能的反向钓鱼策略将推动林木根际微生物工程研究,为揭示杨树-微生物群落的相互关系、菌群进化搭建了研究模型。总之,深入认识多元微生物对林木表型和生理代谢的表观遗传学调控机制将为今后创制新型菌剂并用于高效育苗和抗性育种提供新的思路,具有重要的科学意义和应用价值。

Tree-associated symbiotic microbes and underlying mechanisms of ecological interactions: a case study of poplar

Populus has been increasingly recognized as an important model tree genus, not only due to its wide distribution around the world and an associated great economic and ecological significance, but also the availability of several poplar genomes. Apart from these advantages, Populus is also an ideal organism for investigating physiological and molecular mechanisms underlying tree-microbe interactions, as poplar trees are able to establish multiple symbiotic relationships with a variety of microorganisms thriving in both above-and belowground tissues. Representative poplar-associated beneficial microbes include ectomycorrhizal fungi, arbuscular mycorrhizal fungi, fungal endophytes, nitrogen-fixing bacteria, and plant-growth-promoting rhizobacteria (PGPR), which generally improve poplar growth, nutrition acquisition, and different types of stress tolerance. Rapid progress has been made in understanding the molecular interactions in the development of ectomycorrhizae in the Laccaria bicolor-poplar system and the mechanisms underlying the ectomycorrhizal fungi-mediated poplar abiotic tolerance. Intriguingly, the ecological significance of mycorrhizal helper bacteria and endohyphal bacterial has been recently appreciated. More importantly, a plant microbiome research project was initiated recently; it extensively revolutionizes our understanding of the structure and functions of plant-associated microbiota. The rhizosphere, endosphere, and phyllosphere microbiomes of several poplar species have been uncovered, indicating that both host genotypes and environmental factors influence the microbial community composition. It has been widely accepted that the rhizosphere and endosphere often harbor distinctive microbiota. Promisingly, the strategy of rhizosphere microbiome engineering will shed light on the contributions that soil microbial communities make in improving tree fitness under stress conditions. Looking forward, it will provide a basis for generating robust microbial inoculants that can be utilized in planting seedlings.