外生菌根真菌的共生互作和宿主选择机制研究进展

外生菌根真菌作为树木的共生伙伴,是森林生态系统重要组成部分,在森林天然更新、植物抗逆性形成、协助植物吸收限制性营养等方面扮演重要角色。真菌和植物跨界共生具有复杂的分子互作过程,在共生的不同阶段有不同的分子互作机制,其调控反馈网络还有许多未知。基因组与转录组研究技术和方法的进步,为一些新的信号分子、效应蛋白以及相关通路的发现提供了可能。真菌与宿主植物之间营养转移调控对共生的影响也逐渐受到关注,营养相关的转运蛋白对共生的建立和维持提供了物质基础。真菌的宿主选择机制是值得重点关注的领域,由于外生菌根真菌的多谱系起源和演化史中存在多次宿主转换事件,真菌演化出多样的应对机制用来区分相容性宿主、不相容性宿主和非宿主。通过对不同真菌与宿主植物的组学研究,宿主选择机制研究取得了一定进展。本文对近十年来国内外的研究报道进行梳理与总结,并对未来在该领域的探索方向做出展望。     

内生真菌与宿主植物协同调控砷胁迫作用机制研究进展

丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)和深色有隔内生真菌(dark septate endophytes, DSE)是植物根系中最主要的两大类内生真菌,均可与植物根系形成菌根共生体,在促进植物生长,提高重金属等胁迫抗性方面发挥着重要作用。砷(arsenic, As)及砷化合物具有较强的毒性,可在植物中富集,造成生物链毒害。本团队一直致力于内生真菌与药用植物生长、活性物质合成,砷吸收、积累关系的研究,并取得了一定的进展。结合团队现有研究和前人研究成果,本文分析归纳了砷胁迫条件下,AMF定殖对宿主植物生长和砷吸收、积累的影响;详细阐述了砷胁迫条件下,宿主植物生理活动、抗氧化系统、激素水平、转录水平响应AMF调控的变化。其后,从宿主植物细胞内、外两个方面总结内生真菌与宿主植物协同调控砷胁迫的作用机制,归纳为“生长稀释效应”“菌丝隔离”“螯合过滤”“菌根固定化(mycorrhizal immobilization)”“转运体抑制效应”“生物转化作用”和“保宿主、降氧化”等7项作用机制,并绘制了不同机制之间的作用关系图。DSE-宿主植物调控砷胁迫的研究相...     

植物与病原真菌互作机制研究进展

植物与病原真菌之间的互作是当今植物病理学研究的热点问题之一,相关的研究有望为植物抗病机制的解析和抗病品种的选育奠定理论基础。我们从形态、细胞、生理生化和分子等水平综述了植物与病原真菌互作机制的研究进展。     

豆科植物-根瘤菌共生固氮的免疫调控机制

在长期进化中,根瘤菌与豆科植物形成一种独特的互惠共生关系——共生固氮。根瘤菌-豆科植物共生互作与病原细菌激发植物病原反应极为相似,然而根瘤菌的入侵和定殖并没有激发宿主豆科植物过度的防御反应,植物也进化出特殊的共生信号转导和根瘤发育途径来"邀请"根瘤菌的入侵和定殖。此外,植物防御反应也很大程度上调控根瘤菌与豆科植物共生的宿主特异性。越来越多的研究表明,植物防御反应在调控根瘤菌匹配识别、入侵、定殖以及类菌体发育等方面起关键调控作用。从植物免疫反应角度综述了根瘤菌与豆科植物共生互作的最新进展,通过与病原菌-植物互作的病原反应对比,论述了根瘤中植物感知微生物相关分子模式(MAMP,Microbe-Associated Molecular Patterns)和效应蛋白引起的免疫反应的调控机制。     

内生菌与植物的相互作用：促生与生物薄膜的形成

植物内生菌由于其独特的生态学地位而广受关注,近年来有关植物内生菌与宿主相互作用的研究取得了很大进展.本文综述了植物内生菌通过分泌促生物质、拮抗病原菌等实现与宿主共生互作,同时植物为内生菌提供适宜的黏附表面,使其形成以生物薄膜(biofilm)为主要形式的多细胞聚集体结构以更好地适应周围的生存环境,从而更加高效地对植物产生促生作用.本文论述了内生菌在与植物的互作中形成的多细胞聚集结构在抵抗非生物胁迫方面的独特生理及生态学意义,结合水稻内生成团泛菌YS19形成多细胞聚集体symplasmata现象及其生物学效应,对未来有关植物内生菌的研究方向提出了一些看法.     

龙南钾矿区常见蕨类植物可培养内生真菌的多样性

植物内生真菌作为一类特殊的微生物资源,与宿主在长期的生态系统演化过程中形成了互惠共生关系,通过多样化途径来增强植物体的营养生理和抗性机能,对宿主植物产生多种有益生物学作用,在植物演替过程中具有重要的生态学意义。这种特殊微生物资源近年来倍受关注,而利用植物-真菌共生体强化植物在矿区逆境中生长,提高矿区生物修复效率是一个新的研究热点。为探明钾矿区不同蕨类植物内生真菌的物种多样性、群落组成以及生态分布规律,该研究以芒萁、狗脊、禾秆蹄盖蕨、海金沙、华中铁角蕨、井栏边草和乌蕨等植物为材料,采用组织分离、形态学鉴定等方法,对其内生真菌多样性进行分析。结果表明:从7种植物中共分离获得377株内生真菌,总分离率在2.50%~4.52%之间。经鉴定377个菌株隶属于链格孢属、曲霉属、枝孢菌属和轮枝孢属等25个分类单元,其中链格孢属、曲霉属、枝孢菌属和轮枝孢属等在所有被调查蕨类植物中都有分布,为优势属,共计为185株,占总株数的49.07%,但它们在每种植物的分布存在明显差异;7种蕨类植物内生真菌总定植率为叶高于根状茎(P0.05),多样性指数在0.502~0.867之间,但每种植物及其不同组织部位的内生真菌定植率和多样性指数存在一定的差异;从相似性分析来看,同一个钾矿区不同蕨类植物内生真菌菌群之间的相似性程度较低,相似性系数在0.189~0.587之间。该研究结果不仅丰富了植物内生真菌种质资源,而且为进一步开展植物内生真菌强化宿主植物在钾矿区生长适应机制的研究奠定了基础。     

miRNA介导植物-微生物互作中的调控作用及其研究进展北大核心CSCD

微生物与植物之间存在错综复杂的双向交流和串扰,植物与病原微生物互作直接影响寄主植物的生存状况,而植物和益生微生物互作则有利于宿主的生长和健康,共生微生物也会从中受益。不管是病原微生物还是有益微生物进入植物体内,植物miRNA都会迅速做出响应,同时微生物也可以产生miRNA样RNA(miRNA-likeRNA,milRNA)影响植物健康,可见miRNA(或milRNA)是植物与微生物互作过程中迅速响应的重要媒介分子,其内在机制研究近年来取得了许多进展。文中概述了植物-病原微生物、植物-益生微生物互作中miRNA的调控作用,重点阐述了植物miRNA在植物-病原微生物互作过程中对寄主植物抗病性的调控作用和植物-益生微生物互作过程中对宿主植物生长发育及代谢的调控,以及真菌milRNA对寄主植物的跨界调控作用。     

以杨树为例论述林木共生菌系统及其作用机制

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。     

以杨树为例论述林木共生菌系统及其作用机制

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。     

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。     

Interaction between the endophytic fungus Epichloe bromicola and the grass bromus erectus: effects of endophyte infection, fungal concentration and environment on grass growth and flowering

Epichloe bromicola is an endophytic fungal species that systemically and perennially colonizes intercellular spaces of leaf blades, leaf sheaths and culms of Bromus grass species. E. bromicola causes choke disease in B. erectus, suppressing maturation of most, if not all, host inflorescences. In an investigation of the interaction between fungus and host, we used a quantitative polymerase chain reaction technique to estimate the amount of fungal DNA, and thereby fungal concentration, in host plants. Fungal concentration was directly correlated with vegetative vigour of the plant, as measured by longest leaf length, number of tillers and vegetative above-ground biomass, suggesting that, during vegetative growth, the endophytic fungus is most beneficial for the plant when present in high concentrations. In contrast, the reproduction of the plant, as measured by the number of functional inflorescences, was inversely correlated with fungal concentration: the majority of infected plants, and all that were associated with high concentrations of fungi, were diseased. Thus, the benefit of endophyte infection for the plant is coupled with the disadvantages of infertility. Fungal concentration was shown to be at least in part genetically determined because fungal concentration differed significantly in different plant-endophyte genotype combinations (symbiotum). In a field experiment with normal and CO2-enriched environments, elevated CO2 levels favoured fungal reproductive vigour over host reproductive vigour, suggesting that these plant endophytes would be at a selective advantage in a corresponding environmental-change scenario. We conclude that a dynamic and complex relationship between fungal endophyte infection, fungal concentration, genotype and environment affects growth and fecundity of B. erectus and should contribute to the evolution of these plant-fungal interactions.     

Sugar transporters in plants and in their interactions with fungi

Sucrose and monosaccharide transporters mediate long distance transport of sugar from source to sink organs and constitute key components for carbon partitioning at the whole plant level and in interactions with fungi. Even if numerous families of plant sugar transporters are defined; efflux capacities, subcellular localization and association to membrane rafts have only been recently reported. On the fungal side, the investigation of sugar transport mechanisms in mutualistic and pathogenic interactions is now emerging. Here, we review the essential role of sugar transporters for distribution of carbohydrates inside plant cells, as well as for plant-fungal interaction functioning. Altogether these data highlight the need for a better comprehension of the mechanisms underlying sugar exchanges between fungi and their host plants.     

Balancing multiple mutualists: asymmetric interactions among plants, arbuscular mycorrhizal fungi, and fungal endophytes

Most organisms engage in beneficial interactions with other species; however, little is known regarding how individuals balance the competing demands of multiple mutualisms. Here we examine three-way interactions among a widespread grass, Schedonorus phoenix , a protective fungal endophyte aboveground, Neotyphodium coenophialum , and nutritional symbionts (arbuscular mycorrhizal fungi) belowground. In a greenhouse experiment, we manipulated the presence/absence of both fungi and applied a fertilizer treatment to individual plants. Endophyte presence in host plants strongly reduced mycorrhizal colonization of roots. Additionally, for plants with the endophyte, the density of endophyte hyphae was negatively correlated with mycorrhizal colonization, suggesting a novel role for endophyte abundance in the interaction between the symbionts. Endophyte presence increased plant biomass, and there was a positive correlation between endophyte hyphal density and plant biomass. The effects of mutualists were asymmetric: mycorrhizal fungi treatments had no significant impact on the endophyte and negligible effects on plant biomass. Fertilization affected all three species – increasing plant biomass and endophyte density, but diminishing mycorrhizal colonization. Mechanisms driving negative effects of endophytes on mycorrhizae may include inhibition via endophyte alkaloids, altered nutritional requirements of the host plant, and/or temporal and spatial priority effects in the interactions among plants and multiple symbionts.     

A cryptic microbial community persists within micropropagated Bouteloua eriopoda (Torr.) Torr. cultures

Higher plants are ubiquitously colonized with fungal endophytes that often lack readily detectable structures. This study examines the diverse endophyte population within a single line of micropropagated Bouteloua eriopoda (Torr.) Torr., using microscopy and comparison of internal spacer (ITS) gene sequences obtained from both plant and isolated fungal tissues. Microscopy revealed fungal hyphae and lipid bodies, the majority of which lacked distinguishing characters. Internal transcribed spacer (ITS) sequences amplified from fungal isolates and micropropagated plant tissues were subjected to Bayesian analysis, which clearly distinguished six endophyte taxa.

Results confirm a diverse, cryptic endophyte consortium is retained within this micropropagated plant line. The probability of similar complexity in other plant species is discussed. The development of controlled systems in which to study single plant-fungal interactions within such consortia presents significant technical challenges. However, potential for such systems to reveal species interactions that influence plant growth and development is high.     

Fungal endophytes in a 400-million-yr-old land plant: infection pathways, spatial distribution, and host responses

The Early Devonian Rhynie chert has been critical in documenting early land plant-fungal interactions. However, complex associations involving several fungi that enter into qualitatively different relationships with a single host plant and even interact with one another have not yet been detailed. Here, we studied petrographic thin sections of the Rhynie chert plant Nothia aphylla. Three fungal endophytes (co)occur in prostrate axes of this plant: narrow hyphae producing clusters of small spores; large spherical spores/zoosporangia; and wide aseptate hyphae that form intercellular vesicles in the cortex. Host responses on attack include bulging of infected rhizoids, formation of encasement layers around intracellular hyphae, and separation of infected from uninfected tissues by secondarily thickened cell walls. A complex simultaneous interaction of N. aphylla with three endophytic fungi was discovered. The host responses indicate that some of the mechanisms causing host responses in extant plants were in place 400 million yr ago. Anatomical and life history features of N. aphylla suggest that this plant may have been particularly susceptible to colonization by fungi.     

Effects of host plant environment and Ustilago maydis infection on the fungal endophyte community of maize (Zea mays)

The focus of many fungal endophyte studies has been how plants benefit from endophyte infection. Few studies have investigated the role of the host plant as an environment in shaping endophyte community diversity and composition. The effects that different attributes of the host plant, that is, host genetic variation, host variation in resistance to the fungal pathogen Ustilago maydis and U. maydis infection, have on the fungal endophyte communities in maize (Zea mays) was examined. The internal transcribed spacer (ITS) region of the rDNA was sequenced to identify fungi and the endophyte communities were compared in six maize lines that varied in their resistance to U. maydis. It was found that host genetic variation, as determined by maize line, had significant effects on species richness, while the interactions between line and U. maydis infection and line and field plot had significant effects on endophyte community composition. However, the effects of maize line were not dependent on whether lines were resistant or susceptible to U. maydis. Almost 3000 clones obtained from 58 plants were sequenced to characterize the maize endophyte community. These results suggest that the endophyte community is shaped by complex interactions and factors, such as inoculum pool and microclimate, may be important.     

Effect of different root endophytic fungi on plant community structure in experimental microcosms

Understanding the effects of root‐associated microbes in explaining plant community patterns represents a challenge in community ecology. Although typically overlooked, several lines of evidence point out that nonmycorrhizal, root endophytic fungi in the Ascomycota may have the potential to drive changes in plant community ecology given their ubiquitous presence, wide host ranges, and plant species‐specific fitness effects. Thus, we experimentally manipulated the presence of root endophytic fungal species in microcosms and measured its effects on plant communities. Specifically, we tested whether (1) three different root endophyte species can modify plant community structure; (2) those changes can also modified the way plant respond to different soil types; and (3) the effects are modified when all the fungi are present. As a model system, we used plant and fungal species that naturally co‐occur in a temperate grassland. Further, the soil types used in our experiment reflected a strong gradient in soil texture that has been shown to drive changes in plant and fungal community structure in the field. Results showed that each plant species responded differently to infection, resulting in distinct patterns of plant community structure depending on the identity of the fungus present. Those effects depended on the soil type. For example, large positive effects due to presence of the fungi were able to compensate for less nutrients levels in one soil type. Further, host responses when all three fungi were present were different from the ones observed in single fungal inoculations, suggesting that endophyte–endophyte interactions may be important in structuring plant communities. Overall, these results indicate that plant responses to changes in the species identity of nonmycorrhizal fungal community species and their interactions can modify plant community structure.     

Consequences of simultaneous interactions of fungal endophytes and arbuscular mycorrhizal fungi with a shared host grass

Plants simultaneously associate with multiple microbial symbionts throughout their lifetimes. To address the question of whether the effects of simultaneous symbionts are contingent on the specific identities, we conducted a greenhouse experiment manipulating the presence and identities of arbuscular mycorrhizal fungi (AMF) and fungal endophytes on the shared host grass Elymus hystrix. Each plant host was inoculated with one of two AMF species having varying effects on host growth, or a sterile soil control. Further, we used naturally occurring endophyte‐infected (E+) and uninfected (E–) individuals from two populations of the endophyte Epichloë elymi that varied in their interaction with E. hystrix. We then measured responses of plants, AMF, and fungal endophytes. Overall, we found that the combined effects of AMF and fungal endophytes on plant growth were additive, reflecting the mutualistic quality of each symbiont independently interacting with host plants. However, fungal endophyte infection differentially altered hyphal colonization of the two AMF species and the identity of the coinfecting AMF species affected fungal endophyte fitness traits. The results of this study demonstrate that the outcome of interspecific symbiotic interactions varies with partner identity such that the effects of simultaneous symbioses can not be generalized.     

Role of Diverse Non-Systemic Fungal Endophytes in Plant Performance and Response to Stress: Progress and Approaches

Plant–fungal symbiotic associations are ubiquitously distributed in natural plant communities. Besides the well-studied mycorrhizal symbiosis and grass systemic clavicipitaceous endophytes, recently, nonsystemic and horizontally transmitted fungal endophytes serving as plant symbionts have been increasingly recognized. Pure culture isolation and culture-independent molecular methods indicate that all parts of healthy plant tissues potentially harbor diverse and previously unknown fungal lineages. Limited evidence also supports a hypothesis that endophytic mycobiota dynamics may have a role in evolution of plants. High variability or “balanced antagonism” can be generally characterized with host–endophyte interactions, which implies that the outcome of symbiotic interactions can fall within a continuum ranging from mutualism to commensalism, and ultimately pathogenicity. Despite this complicated system, admittedly, fungal endophytes really endow the host with an extended phenotype. Accumulating facts illustrate that plant nutrition acquisition, metabolism, and stress tolerance may be strengthened or modulated via fungal symbionts. Piriformospora indica, a member of the order Sebacinales, simultaneously confers host resistance to biotic and abiotic stress. The ecological relevance of other fungal groups, including foliar endophytes, root dark septate endophytes (DSEs), some opportunistic and avirulent microsymbionts (for example, Trichoderma and Fusarium), and even uncultured fungi structurally and physiologically integrated with host tissues, are also being deeply exploited. Production of bioactive metabolites by fungi, overexpression of stress-related enzymes, and induced resistance in hosts upon fungal colonization are responsible for direct or indirect beneficial effects to hosts. More knowledge of endophyte-mediated enhancement of host performance and fitness will offer alternatively valuable strategies for plant cultivation and breeding. Meanwhile, with unprecedented loss of biodiversity, discovery of indigenously novel symbiotic endophytes from natural habitats is urgently needed. In addition, we present some approaches and suggestions for studying host–endophyte interactions.     

Endophytic fungus fine‐tunes the persistence strategy of its alpine host grass in response to soil resource levels

An understanding of hereditary endophytic fungi, and the effects on grass persistence strategies (i.e. relative investment in sexual reproduction and vegetative growth) under natural conditions may help to predict how some alpine ecosystems will respond to environmental change. Grass persistence and endophyte maintenance in host populations are closely related, but could become independent due to endophyte loss mechanisms. We used native grass and endophyte populations to test the hypothesis that fungal endophytes manipulate grass persistence strategies to secure endophyte maintenance in plant populations. Two conditions were required to verify this hypothesis: 1) the fungus caused alterations in host plant strategies; and 2) plant phenotypic changes induced by the fungal endophyte increased endophyte transmission. We compared symbiotic (S) and non‐symbiotic (NS) persistence strategies of Festuca eskia (Poaceae), an alpine grass infected by the asexual form of the fungal endophyte Epichloë festucae. We characterised endophyte transmission efficiency, and described vegetative growth and sexual reproduction in a field population that naturally supports approximately 50% S plants. We built a demographic model to estimate plant vegetative growth rates. A correlation between plant persistence strategy, and fungal maintenance was evaluated by increasing soil resource levels. Under natural conditions, S and NS plants exploited different persistence strategies in the same population; S plants exhibited greater vegetative growth than their NS counterparts, while maintaining the same reproductive output. In response to higher soil resource levels, S plants shifted in persistence strategies and phenology, whereas NS plants maintained the same strategies. Therefore, results suggested the fungal endophyte fine‐tuned host persistence strategies according to soil resource level. Finally, we found no direct relationship between the changes induced by fungal endophyte and endophyte transmission. Consequently, fungal endophytes affected host persistence strategies, but did not directly increase endophyte transmission.