The Root-Associated Microbial Community of the World's Highest Growing Vascular Plants.

Upward migration of plants to barren subnival areas is occurring worldwide due to raising ambient temperatures and glacial recession. In summer 2012, the presence of six vascular plants, growing in a single patch, was recorded at an unprecedented elevation of 6150 m.a.s.l. close to the summit of Mount Shukule II in the Western Himalayas (Ladakh, India). Whilst showing multiple signs of stress, all plants have managed to establish stable growth and persist for several years. To learn about the role of microbes in the process of plant upward migration, we analysed the root-associated microbial community of the plants (three individuals from each) using microscopy and tagged amplicon sequencing. No mycorrhizae were found on the roots, implying they are of little importance to the establishment and early growth of the plants. However, all roots were associated with a complex bacterial community, with richness and diversity estimates similar or even higher than the surrounding bare soil. Both soil and root-associated communities were dominated by members of the orders Sphingomonadales and Sphingobacteriales, which are typical for hot desert soils, but were different from communities of temperate subnival soils and typical rhizosphere communities. Despite taxonomic similarity on the order level, the plants harboured a unique set of highly dominant operational taxonomic units which were not found in the bare soil. These bacteria have been likely transported with the dispersing seeds and became part of the root-associated community following germination. The results indicate that developing soils act not only as a source of inoculation to plant roots but also possibly as a sink for plant-associated bacteria.

Diversity and antimicrobial activity of endophytic fungi associated with the alpine plant Saussurea involucrata.

Endophytic fungi are rich in species diversity and may play an important role in the fitness of their host plants. This study investigated the diversity and antimicrobial potential of endophytic fungi obtained from Saussurea involucrata KAR. et KIR. A total of 49 endophytic fungi were isolated from S. involucrata and identified using morphological and molecular techniques. Extracts of fermentation broth from the 49 fungi were tested for antimicrobial activity against pathogenic microorganisms using the agar diffusion method. Forty-eight out of the 49 endophytic fungi were identified and grouped into 14 taxa. Cylindrocarpon sp. was the dominant species isolated from S. involucrata, followed by Phoma sp. and Fusarium sp. Among the 49 endophytic fungi, 9 root isolates having darkly pigmented, septate hyphae were identified as dark septate endophytic (DSE) fungus, and 12 fungi inhibited at least one test microorganism. Moreover, 5 strains showed a broader spectrum of antimicrobial activity and 4 strains displayed strong inhibition (+++) against pathogenic fungi. The results indicate that endophytic fungi isolated from S. involucrata are diverse in species and a potential source of antimicrobial agents.

The promoting role of an isolate of dark-septate fungus on its host plant Saussurea involucrata Kar. et Kir.

A dark-septate endophytic (DSE) fungus EF-37 was isolated from the roots of Saussurea involucrata Kar. et Kir., an endangered Chinese medicinal plant. The molecular identification of the fungus was based on internal transcribed spacer regions and the result showed that EF-37 was congeneric to Mycocentrospora. This study was conducted to clarify the influence of the root endophyte EF-37 on the host plant S. involucrata using material grown in a sterile culture bottle. After cultivation for 40 days, fungal hyphae were found to be branching repeatedly and forming "hyphae nets" in the epidermal layers. Significant differences were detected between the study groups in plant dry weight, plant height, root dry weight, shoot dry weight, and the number of hair root tips. There was a positive effect of endophyte EF-37 on plant root development, with results showing that cortical cells dissolved and formed aerate structures. There was a positive effect of endophyte EF-37 on plant growth, but chlorophyll fluorescence analysis showed that there were no significant differences between the study groups. In addition, analysis of the chemical composition of seedlings showed that the level of rutin was higher in plants cultivated with the EF-37 fungus compared to the controls. This study helps to establish a basis for germplasm conservation and for further investigation of the interaction between dark-septate fungi and this alpine plant.

Interaction between an isolate of dark-septate fungi and its host plant Saussurea involucrata.

A dark-septate endophytic (DSE) fungus EF-M was isolated from the roots of an alpine plant Saussurea involucrata Kar. et Kir. ex Maxim. The fungus was identified by sequencing the PCR-amplified rDNA 5.8S gene and ITS regions. The sequence was compared with similar sequences in the GenBank, and results showed that EF-M was congeneric to Leptodontidium. Resynthesis study was conducted to clarify the relationship between the root endophyte EF-M and the host plant S. involucrata using the material grown in sterile culture bottle. In roots recovered 6 weeks after inoculation, epidermal cells were colonized by intercellular and intracellular hyphae and "microsclerotia" formed within individual cells in the epidermis layers. However, hyphae did not invade the cortex and the stele. There were no profound effects of endophyte EF-M on plant root development, but significant differences were detected in plant height and shoot dry weight between the treatments. The present study is the first report hitherto on DSE fungi in S. involucrata.