Getting to the root of the pattern

For more than a century, scientists have puzzled over how bacteria colonize plant roots and what this colonization means for plant health. Early discoveries, such as the identification of nitrogen-fixing bacteria in the roots of legumes, seeded the modern view that plants orchestrate interactions with their microbial partners. Yet many aspects of how plants manage these relationships remain unclear. On page 44 of this issue, Tsai et al. report that the CHA0 strain of Pseudomonas protegens, a plant growth–promoting bacterium that is commonly used to protect plants from fungal pathogens and insects, is attracted to areas of the root where the amino acid glutamine leaks out (1). This leakage occurs at breaks or natural endpoints in the Casparian strip, a barrier that normally restricts diffusion across root tissues. Their findings highlight how root anatomy can influence the pattern of microbial colonization along plant roots.