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The plant microbiome can be a dual-edged sword to promote plant fitness or cause detrimental effect. Deeper understanding of the underlying regulatory principles holds key to harness the beneficial potential of the microbiome. Through a plant genetic screen in Arabidopsis thaliana, the research group identified a mutant with stunted growth in the presence of the microbiome. The microbial community of this mutant had gone awry, reaching up to 10 times higher microbial load than normal! This abnormality is due to an amplified positive feedback loop involving the phytohormone called jasmonate.

In nature, when a caterpillar takes a bite, the jasmonate pathway is activated to fend off herbivores. Usually, this energy-demanding defense system stays in check under normal conditions to balance between growth and defense. When microbes colonized the plant, they triggered a slight rise in jasmonate. However, in this mutant, the response became hyperactive: heightened jasmonate signaling caused the microbiome to overproliferate, further driving higher jasmonate levels, thus forming an amplified positive feedback loop.

By forcing the jasmonate pathway into an overdrive, the plant boosted defenses against insects but with compromised growth, highlighting the challenge to uncouple the trade-off between growth and defense. As modern agriculture seeks sustainable solutions, strategically tuning plant hormone pathways alongside beneficial microbes, with a combination of chemicals could provide a feasible solution to boost crop yields and stress tolerance.
“Our research demonstrates that plant defense is not simply "on" or "off". Hormone like jasmonate acts as a tunable dial. Unraveling the underlying feedback loops allows us to devise strategies to uncouple the growth-defense trade-off and harness the microbiome for beneficial agricultural services.”

This collaborative work between IPMB, the Max Planck Institute for Plant Breeding Research (MPIPZ) and National Taiwan University was recently published in ISME Journal. The lab of Ka-Wai Ma received financial support from NSTC, German Research Foundation, and Academia Sinica. Co-first authors of this study: Tung-Tse Lu and Miguelito Isip are research assistant and PhD candidate in the laboratory of Ka-Wai Ma, respectively.