Transcriptomics Analysis Reveals an Early Response Gene SlNSP-like Involved in Solanum lycopersicum Response to DC3000 Infection

The hemibiotrophic bacterial pathogen <i>Pseudomonas syringae</i> (<i>Pst</i>) infects a range of plant species and causes enormous economic losses. Despite its agronomic significance, the molecular mechanisms underlying tomato-<i>Pst</i> interactions remain largely uncharacterized. To elucidate these mechanisms, we conducted a comprehensive transcriptomic analysis using infected tomato leaves inoculated with virulent strains <i>Pst</i> DC3000 at relatively early time points. RNA-sequencing of nine libraries identified stage-specific expression patterns, with DEG counts ranging from 484 to 1267 upregulated and from 560 to 844 downregulated genes. Enrichment analysis highlighted significant alterations in metabolic pathways, plant-pathogen interaction networks, and hormone signaling cascades, with marked transcriptional reprogramming observed between the pre- and post-infection stages. A longitudinal analysis of gene expression dynamics identified 15 consistently upregulated and 9 downregulated genes across all post-inoculation time points. Notably, in several candidate genes, a homologous gene of <i>AtNSP2</i>, <i>SlNSP-Like</i> was confirmed to be involved in disease resistance in tomato leaves. SlNSP-Like is localized in the cytoplasm and nucleus, and the transient overexpression of <i>SlNSP-Like</i> tomato plant exhibits significant resistance to <i>Pst</i> DC3000. This study provides valuable insights into the molecular dialogue between tomato and <i>Pst</i>, and the identified regulatory genes and pathways serve as promising targets for breeding disease-resistant tomato cultivars and developing management strategies against bacterial spot disease.