In normal plants, a defense hormone that keeps bad bacteria out from the surface as well as inside the plant's roots and actively recruits the good ones has been detected by researchers. For the study, the researcher team introduced 38 strains of bacteria that they had isolated from roots grown in the wild soil into a sterile clay. The researchers showed that when they grew plants in that synthetic soil, the presence of salicylic acid determined which microbes colonized the roots. The findings are published in the Science Express.
Lead researcher Jeffery Dangl from Howard Hughes Medical Institute (HHMI) in the US said, "With a better understanding of how plants assemble and maintain complex microbial communities, it might be possible to manipulate those communities to increase plant productivity. What we really wanted to understand was how the plant establishes a mutualistic relationship with microbes that it likes, compared to microbes that it does not like."
The researcher team found that the natural level of the defense hormone salicylic acid shapes the microbial community at the root both by keeping certain families out and by letting others in. Dangl said, "This level of salicylic acid gates potential bad guys out, but it is also required as positive signal to attract bacteria. It is not just defense."
Dangl said, "Our survey in the wild soil is essentially an ecology experiment. Now we can build complex communities that recapitulate what we found in those experiments, but are entirely manipulable."
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