<b>Dissecting Plant-Microbe Interactions: MAMP Recognition and Immune Evasion in Solanaceous Hosts</b>

<p dir="ltr">Plants rely on membrane-bound, pattern recognition receptors (PRRs) for extracellular recognition of pathogens as the first line of plant defense. This recognition of conserved microbial signatures, also called microbe-associated molecular patterns (MAMPs), initiates a broad-spectrum immune response known as pattern-triggered immunity (PTI). Overlapping mechanisms in PTI currently serve as the basis for some broad-spectrum resistance strategies; however, PRRs are known to be not only species-specific but also show tissue-specific expression patterns. Here, we identify the downstream PTI responses for three bacterial PRRs in roots of <i>Solanum lycopersicum</i> (tomato) and <i>Capsicum annuum</i> (pepper): FLAGELLIN SENSING 2 (FLS2) FLS3, and the cold-shock protein receptor CORE. Our results show that PTI responses in both tomato and pepper are PRR-specific. In tomato, the common readouts of PTI share overlapping, but distinct, responses to their cognate MAMP elicitor. We find that pepper and tomato share similarities in natural variation of PTI responses, though temporary root growth inhibition is a dominant phenotype for flg22-treated tomato but not flg22-treated pepper. Additionally, our results show that tomato root PTI responses are primarily located in developing tissues. We next shifted our focus from host PTI responses to pathogen-derived MAMPs. Exopolysaccharides (EPS) produced by the soil-borne pathogen <i>Ralstonia solanacearum</i> are required for virulence and have been shown to elicit responses in the host, though the exact mechanism remains unclear. We hypothesized that Ralstonia EPS would be recognized by plant roots and initiate PTI. Surprisingly, we found that crude EPS from two Ralstonia strains can serve as antioxidants for PTI-derived ROS burst in tomato roots. We show that crude EPS from both Ralstonia strains GMI1000 and K60 have different relative abundance in exopolysaccharide types. We show that loss of EPSI production significantly impacts the ability of GMI1000 to alleviate oxidative stress, while K60 relies on alternative mechanisms to mitigate oxidative damage. Together, this work highlights the differential sensitivity and signaling outputs to canonical MAMPs in the Solanaceae and, in turn, provides insight into how bacteria can evade these strategies in the Ralstonia-tomato pathosystem. Such findings will aid in advancing broad-spectrum engineering strategies using PRRs.</p>