丛枝菌根真菌对青杨抗溃疡病生物量和抗病酶活性的影响

本研究以青杨Populus cathayana 1年生扦插苗为试验材料,接种丛枝菌根真菌（arbuscular mycorrhizal fungi,AMF）异形根孢囊霉Rhizophagus irregularis和杨树溃疡病菌聚生小穴壳菌Dothiorella gregaria,测定AMF对青杨根茎叶生物量,丙二醛（MDA）、脯氨酸和茎部纤维素含量,超氧化物歧化酶（SOD）、过氧化氢酶（CAT）、多酚氧化酶（PPO）、几丁质酶、多聚半乳糖醛酸酶和果胶甲基酯酶等抗病酶活性的影响。结果表明,接种AMF可以增加青杨根茎生物量,增加茎纤维素含量来增强树势,降低溃疡病发病率;接种AMF能够显著降低感病杨树茎部和根系MDA含量,增加叶片和根系脯氨酸含量,提高根茎叶PPO活性、茎SOD活性和叶片CAT活性;接种AMF前期可以提高茎和根系几丁质酶和β-1,3-葡聚糖酶活性,也可以提高叶片和茎多聚半乳糖醛酸酶、果胶甲基酯酶活性,接种病原菌条件下AMF效果更加显著。结论认为,AMF通过积累脯氨酸,降低MDA含量,提高SOD、CAT和PPO活性,增强杨树抗溃疡病能力;同时也可提高多聚半乳糖醛酸酶和果胶甲基酯酶活性来抑制病原菌菌丝的生长,减弱菌丝的扩展能力,增强杨树抗病性。     

菌根真菌与兰科植物互作的组学研究进展

兰科植物因其具有丰富的物种多样性和重要的社会经济价值,多年来一直是植物学及生态学界的重点研究对象。菌根真菌对兰科植物的种子萌发、营养吸收和种群动态等多个方面都具有十分重要的作用,因而近年来受到越来越多的关注。探究菌根真菌与兰科植物互作的内在机制是目前兰科菌根研究的一大热点领域,同时也为兰科植物野生资源保护和种群恢复提供了许多新方法与新思路。随着新一代测序技术以及多种组学数据库的发展与建立,菌根真菌与兰科植物互作机制研究已然进入了一个全新的时代。纵观近年来的研究,通过基因组学、转录组学、蛋白质组学和代谢组学等相关技术,人们对兰科菌根共生过程中的种子萌发、营养物质转运、信号转导、宿主免疫和逆境抗性等方面的内在机制有了一定的了解。本文对近十年来国内外采用组学技术研究菌根真菌与兰科植物互作机制方面的研究成果进行了总结和梳理,并对未来该领域的研究进行了展望。     

Symbiotic fungi in roots of Artemisia annua with special reference to endophytic colonizers

Abstract

Advances on plant–fungal interactions reveal that root symbiotic fungi actively modulate host growth, resistance response and secondary metabolism. Artemisia annua has been widely recognized as an important medicinal plant for artemisinin production, yet little is known about the fungal consortium associated with roots of A. annua. In this article, microscopic and culture-dependant methods were used to evaluate the identity and taxonomic affinities of root symbiotic fungi. Morphological evidence confirmed that arbuscular mycorrhizal fungi were dominant fungal group in naturally regenerated roots, but low colonization frequency in planted roots. Dark septate endophytes (DSEs) were easily found, which were characterized with dark pigmented hypha and a sclerotium-like structure in root cortex, and other endophytic fungi also occurred. A total of 36 isolates were recovered. Combined morphological and molecular identification (based on ITS sequences) determined 21 fungal taxa (genotype), which were placed into numerous lineages of Ascomycota. The best BLAST match indicated that almost half of total taxa were closely related to undescribed fungi, some of them may act as novel DSEs but experimental data were warranted. Interestingly, remarkable difference of fungal community associated with two types of roots was examined and no culturable fungi overlapped. Our findings provide some additional evidence that DSEs and other root endophytes may be as common as mycorrhizal fungi. Recovered fungi as raw materials for bioassay of endophytes-mediated promotion of artemisinin content in A. annua will be conducted in further research.     

High mycorrhizal specificity in the mycoheterotrophic Burmannia nepalensis and B. itoana (Burmanniaceae)

Mycorrhizal fungi of mycoheterotrophic Burmannia nepalensis and B. itoana were identified by molecular identification methods based on fungal SSU nrDNA region. In B. nepalensis, RFLP patterns and sequences from all root samples from 14 individuals were identical. A single fungal sequence was also obtained from B. itoana roots from three individuals. Phylogenetic analysis showed that the fungal sequences from these two species are included in Glomeraceae (former Glomus group A). Our results indicate that the two Burmannia species are associated with narrow phylogenetic ranges of arbuscular mycorrhizal fungi.     

Impacts of 3 years of elevated atmospheric CO2 on rhizosphere carbon flow and microbial community dynamics

Carbon (C) uptake by terrestrial ecosystems represents an important option for partially mitigating anthropogenic CO₂ emissions. Short‐term atmospheric elevated CO₂ exposure has been shown to create major shifts in C flow routes and diversity of the active soil‐borne microbial community. Long‐term increases in CO₂ have been hypothesized to have subtle effects due to the potential adaptation of soil microorganism to the increased flow of organic C. Here, we studied the effects of prolonged elevated atmospheric CO₂ exposure on microbial C flow and microbial communities in the rhizosphere. Carex arenaria (a nonmycorrhizal plant species) and Festuca rubra (a mycorrhizal plant species) were grown at defined atmospheric conditions differing in CO₂ concentration (350 and 700 ppm) for 3 years. During this period, C flow was assessed repeatedly (after 6 months, 1, 2, and 3 years) by ¹³C pulse‐chase experiments, and label was tracked through the rhizosphere bacterial, general fungal, and arbuscular mycorrhizal fungal (AMF) communities. Fatty acid biomarker analyses and RNA‐stable isotope probing (RNA‐SIP), in combination with real‐time PCR and PCR‐DGGE, were used to examine microbial community dynamics and abundance. Throughout the experiment the influence of elevated CO₂ was highly plant dependent, with the mycorrhizal plant exerting a greater influence on both bacterial and fungal communities. Biomarker data confirmed that rhizodeposited C was first processed by AMF and subsequently transferred to bacterial and fungal communities in the rhizosphere soil. Over the course of 3 years, elevated CO₂ caused a continuous increase in the ¹³C enrichment retained in AMF and an increasing delay in the transfer of C to the bacterial community. These results show that, not only do elevated atmospheric CO₂ conditions induce changes in rhizosphere C flow and dynamics but also continue to develop over multiple seasons, thereby affecting terrestrial ecosystems C utilization processes.     

Integration of Glomus mosseae with Chromolaena odorata powder for suppression of Meloidogyne incognita on maize (Zea mays L.)

Meloidogyne incognita infestation on maize results in heavy yield loss in farmers’ field. Most of the varieties adopted by subsistence farmers in Nigeria are susceptible to M. incognita. Beside these, the cost of control exceeding the profit from the crop using nematicides and the pollution risk they pose to the environment has necessitated the need for alternatives. Pot and field experiments were, therefore, conducted to investigate the effects of Chromolaena odorata powder and Glomus mosseae (a mycorrhizal fungus) on M. incognita pathogenicity on maize. Hybrid Oba super II improved maize variety adopted by local farmers was selected for the study. Maize plants were grown with G. mosseae (5 spores/g of soil) and soil amended with C. odorata powder (1% w/w) singly and in combination. Two weeks after emergence, Test plants were inoculated with 5000 M. incognita eggs. Sixty days after planting, destructive samples were assessed for root gall symptom and severity, and nematode population. Results show that G. mosseae and C. odorata powder were effective in controlling the population of M. incognita and the root knot nematode symptom and gave the highest yield parameters in combination. Single application of G. mosseae and C. odorata powder was similar in the effect on M. incognita and maize yield. Combination of G. mosseae and C. odorata powder may become a viable alternative to nematicide in managing M. incognita pathogenicity on maize as C. odorata powder may serve as a carrier medium for G. mosseae.     

Involvement of auxin pathways in modulating root architecture during beneficial plant–microorganism interactions

A wide variety of microorganisms known to produce auxin and auxin precursors form beneficial relationships with plants and alter host root development. Moreover, other signals produced by microorganisms affect auxin pathways in host plants. However, the precise role of auxin and auxin‐signalling pathways in modulating plant–microbe interactions is unknown. Dissecting out the auxin synthesis, transport and signalling pathways resulting in the characteristic molecular, physiological and developmental response in plants will further illuminate upon how these intriguing inter‐species interactions of environmental, ecological and economic significance occur. The present review seeks to survey and summarize the scattered evidence in support of known host root modifications brought about by beneficial microorganisms and implicate the role of auxin synthesis, transport and signal transduction in modulating beneficial effects in plants. Finally, through a synthesis of the current body of work, we present outstanding challenges and potential future research directions on studies related to auxin signalling in plant–microbe interactions.     

Arbuscular mycorrhizal fungi reduce growth and infect roots of the non‐host plant Arabidopsis thaliana

The arbuscular mycorrhizal (AM) symbiosis is widespread throughout the plant kingdom and important for plant nutrition and ecosystem functioning. Nonetheless, most terrestrial ecosystems also contain a considerable number of non‐mycorrhizal plants. The interaction of such non‐host plants with AM fungi (AMF) is still poorly understood. Here, in three complementary experiments, we investigated whether the non‐mycorrhizal plant Arabidopsis thaliana, the model organism for plant molecular biology and genetics, interacts with AMF. We grew A. thaliana alone or together with a mycorrhizal host species (either Trifolium pratense or Lolium multiflorum) in the presence or absence of the AMF Rhizophagus irregularis. Plants were grown in a dual‐compartment system with a hyphal mesh separating roots of A. thaliana from roots of the host species, avoiding direct root competition. The host plants in the system ensured the presence of an active AM fungal network. AM fungal networks caused growth depressions in A. thaliana of more than 50% which were not observed in the absence of host plants. Microscopy analyses revealed that R. irregularis supported by a host plant was capable of infecting A. thaliana root tissues (up to 43% of root length colonized), but no arbuscules were observed. The results reveal high susceptibility of A. thaliana to R. irregularis, suggesting that A. thaliana is a suitable model plant to study non‐host/AMF interactions and the biological basis of AM incompatibility.