Bacteria live everywhere, and we're starting to understand how they affect the biology of animals and plants. This comes at a time when extreme weather events are becoming more common. Scientists have now identified bacteria that live on plants that like the desert. These microorganisms may become a useful tool in agriculture, and might encourage important crops to keep producing food through heatwaves and droughts.
While some plants are naturally resistant to heat, it's expensive and time-consuming to engineer or breed crops that are heat-tolerant. Microbes that live in the root systems of plants have been shown to help plants survive exposure to excessive heat, high salt levels, or drought; they might offer a faster and less laborious way to improve agriculture as growing conditions become more unpredictable. In a new study published in EMBO Reports, scientists are learning more about putting this idea into practice.
"Beneficial bacteria could become one of the quickest, cheapest and greenest ways to help achieve sustainable agriculture," said first study author and postdoctoral researcher Kirti Shekhawat. "However, no long-term studies have proven they work in the real world, and we haven't yet uncovered what's happening on a molecular level," she noted.
In this study, the researchers focused on SA187, a beneficial microbe that lives in the roots of a desert shrub called Indigofera argentea. The scientists coated wheat seeds with SA187 and planted them along with untreated seeds in a lab garden. After six days, the crops were exposed to 44 degree Celsius heat for two hours. "Any longer would kill them all," said Shekhawat.
The investigators found that while the untreated seeds had leaf damage and stopped growing, the treated seeds did not seem to be affected by the heat, and flourished. This suggested that the bacteria helped the seeds tolerate the heat exposure that had killed the other plants.
"The bacteria enter the plant as soon as the seeds germinate, and they live happily in symbiosis for the plant's entire life," explained Shekhawat.
The scientists continued to grow the wheat they'd created for several years in Dubai fields, where it can get as hot as 45 degrees Celsius (113 degrees Fahrenheit). Typically, wheat is only grown there during the winter. But the bacteria-treated plants withstood the heat, and even produced 20 to 50 percent more wheat than what was expected.
"We were incredibly happy to see that a single bacterial species could protect crops like this," said Shekhawat.
Investigating further with a common model organism in plant research, the scientists identified which plant genes were affected by the bacteria. When the model plant Arabidopsis was exposed to heat with and without the microbe treatment, the researchers determined that the bacteria generate metabolites, which are converted into a plant hormone called ethylene. That promotes the activity of heat-resistance genes in the plant.
"Essentially, the bacteria teach the plant how to use its own defense system," explained Shekhawat.
"We have just scratched the surface of this hidden world of soil that we once dismissed as dead matter," said study leader Professor Heribert Hirt of King Abdullah University of Science and Technology (KAUST). "Beneficial bacteria could help transform an unsustainable agricultural system into a truly ecological one."
Sources: AAAS/Eurekalert! via KAUST, EMBO Reports