Amazing stuff!
"Although plants ... actually chat with each other quite often through volatile organic compounds, electrical signals, and mycorrhizal networks. One of their most common topics of gossip: potential threats. ... Turns out that maize, one of the world’s most valuable crops, is especially chatty when planted in a crowded field—chemical communication protects the plants from disease and herbivores.
While studying densely planted corn fields, researchers noticed that even though stalks in the inner rows were smaller, they were much safer from herbivores than those on the outskirts. ... In greenhouse experiments, the team found that corn planted in soils that previously had grown the plants close together gained increased resistance to insects, nematodes, and pathogens, too, indicating that the crowded plants had altered the soil they grew in.
Using chemical, physiological, and genetic analyses ... on the corn’s methods: Densely planted shoots release the volatile linalool, which increases production of the hormone jasmonate. Jasmonate goes on to promote the release of benzoxazinoids, which foster a lasting change in the soil microbiome; this leads to both pest protection and hindered growth after only three days of high-density planting. ..."
From the editor's summary and abstract:
"Editor’s summary
Maize plants emit a volatile gas called linalool, which can influence the growth and development of neighboring plants. Guo et al. found that at high planting densities, high linalool concentrations triggered neighboring plants to release benzoxazinoids into the soil (see the Perspective by Schandry and Becker). These compounds cause the soil microbiota to change composition, with knock-on effects for plants that are subsequently grown there. The altered microbiome enhances defense responses to herbivores but reduces plant growth. These findings demonstrate the implications of high planting density on multiple facets of the plant growth environment. ...
Structured Abstract
INTRODUCTION
Planting crops more densely increases overall yields, but it also raises the risk of pest and pathogen outbreaks. Although plants can modify their architecture to adapt to crowded conditions, how they adjust their immune responses remains largely unknown. ...
RATIONALE
Plants release chemical cues, such as volatiles, that inform neighbors of environmental conditions. One such compound, linalool, is a constitutively emitted leaf volatile in maize and other grasses. ...
RESULTS
Field surveys revealed that maize plants in the inner rows of densely planted fields suffered less herbivore damage than those at the edges but that they also had reduced growth. Laboratory soil–transplantation experiments confirmed that soils conditioned by high-density plantings decreased plant biomass while enhancing resistance to insects, nematodes, and pathogens. These effects extended across genotypes and species.
Volatile profiling identified linalool as a key compound increasing with planting density. Exposure of maize to synthetic linalool reproduced the feedback effects, which required the presence of a living plant. Mechanistically, linalool activated jasmonate signaling in roots and up-regulated genes that drive the biosynthesis and exudation of the specialized metabolite HDMBOA-Glc. This exudate reshaped the rhizosphere microbiome, selectively enriching bacteria that suppressed plant growth but increased resistance in subsequently grown plants. Soil sterilization and microbial inoculation confirmed that these microbes were essential for the feedback loop.
In plants grown in linalool-conditioned soil, defense-related signaling, particularly salicylic acid signaling, was up-regulated, whereas growth-promoting metabolic pathways were down-regulated. Plants lacking salicylic acid signaling did not show growth-defense trade-offs, confirming salicylic acid’s role in expressing the feedback-triggered defense.
CONCLUSION
This study uncovers a volatile-triggered feedback mechanism through which maize adapts its defense in crowded environments. The constitutive emission of linalool primes neighboring plants by activating root jasmonate signaling, promoting HDMBOA-Glc exudation, and altering the rhizosphere microbiome. This, in turn, leads to elevated defense and suppressed growth in subsequent plants through salicylic acid signaling. These findings shed light on how plants integrate aboveground cues and belowground processes to optimize defense in high-density settings. Harnessing this natural defense pathway through breeding, microbial inoculants, or synthetic biology could enable the development of crops that are more resilient and require fewer chemical inputs."
Linalool-triggered plant-soil feedback drives defense adaptation in dense maize plantings (no public access)
Model illustrating how dense planting triggers plant-soil feedback to enhance maize resistance.
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