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A defensive plant hormone located in the leaves helps to sculpt the microbiome, or community of microorganisms, surrounding a plant's roots, researchers say. This finding demonstrates how plant immunity can drive specific families of bacteria to colonize a plant's roots, where they might boost a plant's fitness or productivity by improving access to nutrients or enhancing tolerance to environmental stress, for example. Botanists have struggled to explain how plants gate access to their roots, allowing only beneficial, non-pathogenic microbes to colonize them and blocking unwanted parasites. Sarah Lebeis and colleagues performed a series of experiments with the model plant, Arabidopsis thaliana, and discovered that a central regulator of the plant's immune system above ground -- the hormone salicylic acid -- also acts as a bacterial bouncer below ground. When the synthesis or the signaling of salicylic acid was eliminated in A. thaliana mutants, the researchers found that microbes in the plants' roots and rhizosphere -- the layer of soil directly adjacent to the roots -- rearranged themselves. The abundance of certain bacterial families increased while others decreased and some disappeared altogether, according to the researchers. Physiological differences between the microbes appear to influence their participation in a plant's root microbiome, they say. Taken together, these findings imply that salicylic acid is required to assemble a normal, commensal root microbiome. The findings could be used to enhance crop production and sustainability.
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Article #15: "Salicylic acid modulates colonization of the root microbiome by specific bacterial taxa," by S.L. Lebeis at University of Tennessee in Knoxville, TN; J.L. Dangl at Howard Hughes Medical Institute in Knoxville, TN; S.L. Lebeis; S.H. Paredes; D.S. Lundberg; N. Breakfield; J. Gehring; M. McDonald; C.D. Jones; J.L. Dangl at University of North Carolina in Chapel Hill, NC; S. Malfatti; T. Glavina del Rio; S.G. Tringe at DOE Joint Genome Institute in Walnut Creek, CA; J.L. Dangl at Carolina Center for Genome Sciences in Chapel Hill, NC; D.S. Lundberg at Max Planck Institute for Developmental Biology in Tübingen, Germany; N. Breakfield at NewLeaf Symbiotics in St. Louis, MO; J. Gehring at University of California, Berkeley in Berkeley, CA; S. Malfatti at Lawrence Livermore National Laboratory in Livermore, CA.
Journal
Science