Fuente: PubMed "Tomato process" Appl Environ Microbiol. 2026 Jul 27:e0068126. doi: 10.1128/aem.00681-26. Online ahead of print.ABSTRACTPlants host diverse microbial communities across spatially distinct foliar niches. For hemibiotrophic pathogens, the epiphytic leaf surface and the apoplast impose contrasting physiological constraints that shape infection strategies. We investigated how these environments program the transcriptional responses of a tomato pathogen, Xanthomonas perforans (Xp), and how virulence, metabolism, and regulation are coordinated across space and time during disease progression. By selectively enriching and profiling the transcriptome of a pathogen from the leaf surface and apoplast, we uncovered pronounced niche-specific and colonization stage-specific gene expression patterns. Early epiphytic colonization features activation of chemosensing and motility to promote relocation, alongside iron and phosphate acquisition, DNA and protein repair, quorum sensing, phenylalanine degradation/tyrosine conversion consistent with countering phenylpropanoid defenses, osmotic and oxidative stress mitigation, DNA exchange machinery, and type VI secretion-mediated microbial competition. Upon entry into the apoplast, Xp shifts toward active metabolism and replication, accompanied by investment in type II and III secreted virulence factor expression, together with countermeasures against host-mediated nutrient sequestration. Late apoplastic infection triggers renewed stress responses and reactivation of motility, consistent with preparation for dissemination. Across both niches, oxidative and nutrient stress responses are prominent, but the specific gene sets engaged differed by environment. Together, this work provides a mechanistic, systems-level model of how a foliar pathogen perceives and adapts to structured host niches, revealing spatiotemporal regulatory logic that coordinates survival on the leaf surface with virulence and growth in the apoplast. This framework provides broadly applicable insights into ecology and virulence programming in planta.IMPORTANCEFoliar bacterial pathogens face a series of shifting challenges as they move from the leaf surface into the protected interior. Xanthomonas perforans is a major tomato pathogen, yet how it engages in molecular dialog with the host has remained largely unclear. Reverse genetics approaches have revealed individual virulence factors, but they capture only fragments of a much larger process. By profiling pathogen transcriptomes in distinct microhabitats, we show how X. perforans reprograms its physiology during infection, adjusting motility, stress tolerance, metabolism, and virulence. This stage-resolved perspective uncovers the logic behind the infection cycle, revealing coordinated gene expression programs and regulatory modules during niche transitions. Our findings also demonstrate that ecologically similar foliar pathogens do not solve the same problems in the same way. Although X. perforans and Pseudomonas syringae occupy comparable niches, they adopt distinct metabolic and stress-response strategies, and plants perceive and respond to them differently. Such contrasts highlight how even closely related infection lifestyles can trigger unique molecular dialogs with the host. By illuminating nutrient limitations, and regulatory programs that shape infection from the outset, this work provides a systems-level view of disease establishment and identifies vulnerable points in the infection cycle that could be leveraged for targeted disease management.PMID:42505097 | DOI:10.1128/aem.00681-26