Plant and Fungal Symbiosis in Drought Conditions

 In plants there can be many reactions to stress. In particular, this blog will focus on fungus and how it can benefit the plant by lessening symptoms caused by drought stress. In terrestrial biomes, water and temperature conditions are highly variable, and extreme water and temperature conditions affect the growth, survival and reproduction of plants. "More than 90% of wild terrestrial plant species are estimated to have close ecological interactions with mycorrhizal fungi." http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0086566
 http://www.sciencedirect.com/science/article/pii/S1874939911001428

http://www.americanforests.org/wp-content/uploads/2014/10/3.-Diagram-of-seedling-and-ectomycorrhizal-fungi-CCripps_web.jpg

"Successful plant-fungal symbioses involve at least three events: penetration by the fungus into plant tissues; colonization of plant tissues by the invading fungus; expression of a fungal symbiotic lifestyle." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3121976/ Drought can negatively affect many aspects of plant physiology and can inhibit plant growth and reduce photosynthesis which impacts the flow of sugars from the host plant to its fungal partner. Because of this symbiotic relationship, VAM fungi have a mutual interest in reducing drought stress for the host plant. VAM fungi react to drought stress by expanding the plant roots and adding their own expansive network of absorbing strands to probe the soil for water and the minerals it carries. VAM fungi can also affect the opening and closing of the plant stomates. Under drought stress, the plant will close the stomates to reduce the loss of water. VAM fungi can affect the closure of the stomates and help the plant conserve more water.  Closing of the stomates creates more tugor pressure in the plant by preventing water loss and thereby delaying or preventing wilting. Delayed wilting and water conservation support cell function, allowing growth and photosynthesis to continue.  http://www.lebanonturf.com/education/mycorrhizal-fungi-can-reduce-the-effects-of-drought-on-plants Many drought-inducible genes have been studied and identified, which can be classified into two major groups: proteins that function directly in abiotic stress tolerance and regulatory proteins, which are involved in signal transduction or expression of stress-responsive genes. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3121976/

http://scialert.net/fulltext/?doi=jbs.2013.112.122&org=11

Mycorrhizal fungi also improve mineral absorption in plants. "As a result, VAM fungi can also produce increased or sustained yields with reduced fertilizer application. This can reduce farm expenses and cut down on pollution of surface and ground water. The magnitude of these effects varies with different crops and different farm practices." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4717633/

https://greenbeanconnection.files.wordpress.com/2013/11/mycorrhizal-fungi-700.jpg

 The genetic basis of symbiotic communication is not yet known, some studies suggest the subtle differences in host genomes have obvious effects on the result of symbiotic interactions. For example, within the geothermal soils of Yellowstone National Park, WY, a plant species (Dichanthelium lanuginosum) has been found to be colonized by one endophyte (Curvularia protuberata).C. protuberate extend heat tolerance to the host plant. Neither the fungus nor the plant can survive separate from one another when exposed to heat stress >38°C. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3121976/ 

http://www.nature.com/nrmicro/journal/v9/n2/fig_tab/nrmicro2491_F3.html

Because plant growth and development cannot be adequately described without acknowledging microbial interactions more studies need to be conducted on plants and their symbiotic systems  to fully understand the functions and contributions of all symbionts for better plant health, production and protection. 
These types of studies could have heavy implications for future by providing the means to establish healthy plant communities to provide food for an ever growing population that is under a global climate change.