Gardeners and farmers know that roundworms are a source of headache. Nematode infestation causes damage in plants by infecting its roots and eventually killing the plant. An estimated $100 billion in crop damage is caused by these tiny, ubiquitous roundworms. However, according to a groundbreaking new study, plants are able to manipulate the pheromones of these worms to be able to repel infestations.
The study was done by a team of researchers led by Frank Schroeder of the Boyce Thompson Institute and published in Nature Communications. The group analyzed a series of chemicals that are called ascarosides -- the chemical which the worms use to communicate with each other. Surprisingly, the researchers found that plants are also mimicking the worm's way of communicating with each other by producing ascarosides and excreting the metabolites into the soil. Schroeder explains that aside from sensing the presence of the roundworms, the plants somehow learned a foreign language. The plant uses this language to spread 'propaganda' to drive the nematodes away.
Scientists explored this study as a follow-up to their previous work involving the plants' reaction to ascr#18 also known as the predominant ascaroside secreted by nematodes. Whenever around the said chemical, plants will bolster up its immune system to protect themselves against pathogens. "When ascr#18 was given to plants, the chemical disappears over time." Murli Manohar, the lead author of this particular study explains." From this observation and various literature supporting the theory that plants are able to modify pest metabolites, researchers are thinking that plants and worms communicate through a small molecule that sends the messages to each creature.
To test their theory, the researchers used three types of plants -- Arabidopsis, wheat, and tomato -- and treated them with ascr#18. After that, the researchers analyzed and compared compounds between treated plants and those that are untreated with ascr#18 where they were able to identify three metabolites of ascr#18 and the most abundant of these three were ascr#9.
The roots of Arabidopsis and tomato secreted the three metabolites into the soil. The effect was immediate: the mixture of 90% ascr#9 and 10% ascr#18 was able to drive away roundworms from the roots of these plants. The possible explanation to this is that nematodes in the soil receive the signal from the plants thinking that it was already occupied by other nematodes. It is possible that the worms evolved to tamper plant metabolism to prevent overpopulation. However, scientists explain it is also possible that this is the plant's way of adapting and saving itself from these pests. According to Manohar, this is a dimension of the plant-pest relationship that was not seen before. Manohar also explains that it is possible that plants have a similar type of chemical communication system with other pests.
Schroeder clarifies that ascr#9 and ascr#18 can be used for crop protection but is also safe to use ascr#18 directly because it prepares the plant to respond to the pathogen quickly and strongly. "There should be no cost to the plant in terms of reduced growth, yield or other problems." He said. He and his team were also able to discover an ancient interaction through the plant's processing of ascr#18 through the peroxisomal β-oxidation pathway. "All nematodes make ascarosides, and plants have had millions of years to learn how to manipulate these molecules," Schroeder explains. He also emphasized that plants are not passive but instead are very much active in participating with their surroundings.