Nitrogen Uptake Between Fungi and Orchids

The Science

Orchids are an example of an experimentally tractable plant that is highly dependent on its relationship with its mycorrhizal fungal partners for nutrient supply. In a recent study, researchers, for the first time, identified some genetic determinants potentially involved in nitrogen uptake and transfer in orchid mycorrhizas.

The Impact

This study provides a model system, amenable to experimental manipulation, for plant-fungi nutrient exchanges on a symbiotic level. It also offers insights into how host plants benefit from the mutualistic relationships formed with soil fungi that can expand their habitat range. Understanding these vital relationships may shed light on microbial symbioses applicable to growing bioenergy feedstock plants.

Summary

Orchids, like the majority of terrestrial plants, form symbiotic relationships between their plant roots and soil fungi, known as mycorrhizal associations. However, unlike other terrestrial plants, orchids rely on their mycorrhizal fungal partners for nutrient supply during the feed germination and development stages. Following these stages, most orchid species develop leaves and are capable of self-nourishment, whereas some species continue to rely on their fungal partners for an organic carbon supply. In this study, a team led by University of Turin researchers investigated the orchid mycorrhizal fungus Tulasnella calospora as both a free-living mycelium and in symbiosis with the photosynthetic orchid long-lipped serapias, or Serapias vomeracea. For the first time, researchers looked at the fungal genes that may have been involved in both the uptake and transfer of nitrogen to the host plant. RNA sequencing for the project was performed at the U.S. Department of Energy’s (DOE) Joint Genome Institute (JGI), a DOE Office of Science user facility.

The team also used JGI’s fungal genome database MycoCosm to identify fungal genes coding for proteins that were involved in nitrogen uptake and transfer. They found that the T. calospora genome has two genes coding for ammonium transporters and several genes coding for amino acid transporters, proteins that play roles in the nitrogen nutrient pathway. Overall, the orchid mycorrhizal fungi’s use of nitrogen may broaden the habitat ranges of orchids, allowing them to grow in a variety of soil types. Of more general interest to the DOE, this study provides important insights for this process and furthers understanding of plant-microbial symbioses that are vital for plant health and may inform understanding of microbial symbioses relevant to bioenergy feedstock plants.

Principal Investigator(s)

Silvia Perotto
University of Turin
[email protected]

Funding

U.S. Department of Energy Office of Science
Ministry of Education, Universities, and Research (Italy)
University of Turin
‘Compagnia di San Paolo’ (Torino, Italy)
Laboratory of Excellence Advanced Research on the Biology of Tree and Forest Ecosystems (ARBRE)

References

Fochi, V., W. Chitarra, A. Kohler, S. Voyron, V. Singan, E. Lindquist, K. Berry, M. Girlanda, I. V. Grigoriev, F. Martin, R. Balestrini, and S. Perotto. 2017. “Fungal and Plant Gene Expression in the Tulasnella calospora—Serapias vomeracea Symbiosis Provides Clues About Nitrogen Pathways in Orchid Mycorrhizas,” New Phytologist 213(1), 365-79. DOI: 10.1111/nph.14279.