Tomato Roots Exhibit Development-Specific Responses to Bacterial-Derived Peptides

To combat soilborne pathogens, roots activate pattern-triggered immunity (PTI) through pattern-recognition receptors (PRRs) that recognise microbe-associated molecular patterns (MAMPs). Root PTI pathways can differ from their above-ground counterparts and have been well-characterised in the model plant Arabidopsis thaliana but are not well-defined in crops. Gene repurposing coupled with differences in root tissues and root architecture in tomato species (Solanum lycopersicum and S. pimpinellifolium) led us to hypothesise that signalling pathways of Solanaceous-specific PRRs diverge from canonical pathways. The objective of this study was to characterise PTI signalling pathways and responses (ROS, MAPK, gene expression, and growth inhibition) in roots of wild and domesticated tomatoes downstream of three immune receptors: the well-conserved SlFLS2 and the Solanaeceous-specific FLS3 and CORE. We find that Solanum root PTI responses are concentrated in early differentiating root regions compared to late differentiating regions or whole roots, and that FLS3 and CORE signalling pathways are overlapping but distinct from each other and from FLS2. Although the early differentiating root region had strong PTI responses across Solanum cultivars and species, different genetic backgrounds varied in their response dynamics. Our results underscore the complexity of PTI signalling across species and highlight the developmental-stage specificity of tomato root immunity.