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Arbuscular Mycorrhizal Fungi in a Changing Global Environment
Angelard, C., Tanner, C.J., Fontanillas, P., Niculita-Hirzel, H., Masclaux, F. and Sanders, I.R. 2014. Rapid genotypic change and plasticity in arbuscular mycorrhizal fungi is caused by a host shift and enhanced by segregation. The International Society for Microbial Ecology Journal 8: 284-294.

Arbuscular mycorrhizal fungi (AMF) penetrate the cortical cells of the roots of vascular plants and help them capture nutrients such as phosphorus, sulfur, nitrogen and various micronutrients from the soil in which they grow; and in this regard the authors note that AMF "are among the most abundant symbionts worldwide ... associating with over 60% of all plant species for the last 460 million years and across the majority of terrestrial biomes," citing, in this regard, the work of Redecker et al. (2000) and Smith and Read (2008). And they further note that via this association, AMF both "improve plant growth" and "protect plants against pathogens and herbivores," while at the same time adding that AMF diversity plays "a key role in ecosystem productivity and plant diversity," as demonstrated by the studies of Harrison (1997) and van der Heijden et al. (1998).

What was done
Hypothesizing that (1) "AMF respond rapidly to a change of environment (plant host) through changes in the frequency of nucleotypes," that (2) "genotypically novel offspring exhibit different genetic responses to environmental change than the parent," and that (3) "genotypically novel offspring exhibit a wide range of phenotypic plasticity to a change of environment," Angelard et al. "subjected AMF parents and offspring to a host shift," working with hyphae and spores produced vegetatively from AMF lines growing on Daucus carota (carrot) and Solanum tuberosum (potato).

What was learned
The six scientists report that "quantitative molecular analyses showed that a host shift induced a significant alteration in relative allele frequencies among initial and segregated AMF lines," and they say that "this result shows that alleles were likely to be located on different nuclei inside the fungus and that the different nuclei had changed frequency in response to the host shift."

What it means
Angelard et al. say their results demonstrate that (1) "AMF can rapidly undergo genotypic change in response to the environment they experience," that (2) "changes in nucleotype frequency can have a role in performance in a new environment," that (3) "the ability to rapidly change genotype composition is important as it provides a mechanism for the fungus to be plastic when growing from plant to plant," and that (4) "the ability to alter nucleotype frequencies offers a greater potential for adaptability to the different environments the fungus experiences than that which could occur by plasticity in one genome," all of which suggests that plants associated with AMF may be much more capable of adjusting to changing environments than has long been believed possible.

Harrison, M.J. 1997. The arbuscular mycorrhizal symbiosis: An underground association. Trends in Plant Science 2: 54-60.

Redecker, D., Kodner, R. and Graham, L.E. 2000. Glomalean fungi from the Ordovician. Science 289: 1920-1921.

Smith, S.E. and Read, D.J. 2008. Mycorrhizal Symbiosis. Academic Press, San Diego, California, USA.

van der Heijden, M.G.A., Klironomos, J.N., Ursic, M., Moutoglis, P., Streitwolf-Engel, R., Boller, T., Wiemken, A. and Sanders, I.R. 1998. Mycorrhizal fungal diversity determines plant biodiversity, ecosystem variability and productivity. Nature 396: 69-72.

Reviewed 16 April 2014