What it is
Studying how plant roots shape their microbiome, the authors show that endodermal Casparian strips, which form the root's extracellular diffusion barrier, restrict nutrient leakage into the rhizosphere and thereby control where rhizobacteria colonize. They identify vasculature-derived glutamine leakage as a major bacterial chemoattractant and enhancer of proliferation, defining a previously unknown pathway for root exudate formation. Bacteria unable to sense amino acids are less attracted to leakage sites, and roots with defective Casparian strips show bacterial overproliferation that depends on the bacteria's capacity to metabolize amino acids.
Why it matters
Root exudates are known to assemble the microbiome that supports plant function and stress resilience, but how specific exudates set the spatial pattern of colonization had been largely unknown. This work pinpoints localized glutamine leakage, gated by the Casparian strip diffusion barrier, as a specific chemical signal that positions colonizing bacteria. It casts the endoderm's nutrient restriction as a control point for microbial colonization and assembly.
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Filed underLegume Nitrogen Fixing Symbiosis, Plant-Microbe Interactions and Immunity, Plant Molecular Biology Research