Thirsty Plants Rely on Fungus for Help
There are naturally occurring drought tolerant plants that are able to grow in very inhospitable environments such as mountain sides and by geo thermal vents. The reason that plants can live in this sort of environment is because of the microbiome - the collection of fungi, bacteria and viruses that live in the root systems of every plant. In exchange for nutrition, the symbiotic microorganisms help the plants take up nitrogen from the soil and protect them from heat, drought and disease-causing organisms.
This gave Russell Rodriguez (of the University of Washington in Seattle), and Regina Redman, (Rodriguez's collaborator) and partner a brain wave. By transferring the microbiome of a drought-tolerant plant to a normal plant would help it use less water.
In an experiment, Rodriguez and his colleagues isolated spores from the microbiome of a grass which grows near thermal springs in temperatures of up to 70 degrees, and applied them onto wheat seeds, which normally grow at temperatures up to 38 °C. With the spores, the wheat could grow at 70 °C and needed up to 50 per cent less water than normal (The ISME Journal, DOI: 10.1038/ismej.2007.106).
But these microbiomes don’t just help with heat and drought. They can help plants overcome a range of different environmental stresses. The group have also isolated microbiomes from a salt-loving dunegrass, and a strawberry plant that grows at high altitude at temperatures as low as 5 °C. Rice plants that had been sprayed with the fungi became able to tolerate salt and cold, respectively. They also grew five times larger and needed half the water of normal plants (PLoS One, DOI: 10.1371/journal.pone.0014823).
The team found that the application of the endophytes (fungi that grow inside the plant) to the rice, made it express genes involved in stress-resistance and drought-tolerance. Within 24 hours of being sprayed, the seeds began sprouting a greater number of longer roots than untreated seeds.
Genetically engineering of plants to become drought-tolerant involves switching on metabolic pathways one at a time, a slow and often ineffective process. Whereas the fungi appear to activate them all in one go.
What's more, lab tests suggest endophytes do not harm the plant in wet conditions, in contrast to drought-tolerant GM plants, which tend to grow poorly when the weather turns.
So this technique has definite advantage over GM crops: farmers could decide whether to spray their seeds with them at the beginning of the planting season rather than gambling on a drought-tolerant variety.
So far from GM being the only way to ‘Feed the World’ a faster, environmentally sound, and uncontroversial method of utilising microbiomes might be a fast way to reach the goal of doubling global food production by 2050.
With droughts such as the one affecting the US expected to become more frequent over coming decades, plant biologists aren't hopeful that they can meet this goal through genetic engineering.
Mary Lucero, at New Mexico State University says; “To meet food demands, we need to adapt quickly. Microbial communities have always adapted quickly” Rather than isolating individual species of fungi, Lucero believes it might be more effective to harness the whole microbial community by mulching up drought-tolerant plants' roots and growing crops in them. One thing is for sure according to Lucero, “Biotechs can't work fast enough to meet the pressures of 7 billion people and climate change.”
Thermotolerance Generated by Plant/Fungal Symbiosis Redman, et al. Science 22 November 2002: 1581.DOI:10.1126/science.1078055