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Plant pathogenic Pseudomonas species cause a variety of diseases in plants. Each Pseudomonas species employs different virulence factors and strategies for successful infection. Moreover, even the same bacterial pathogens can differentially utilize virulence factors against various host plants. However, there has been relatively less emphasis on comparing the infection strategies of a single bacterial pathogen on different hosts and different bacterial pathogens on a single host. Here, we investigated plant–pathogen interactions using two Pseudomonas species, Pseudomonas cannabina pv. alisalensis (Pcal) KB211 and Pseudomonas syringae pv. tomato (Pst) DC3000, and their host plants, cabbage and tomato. Our findings reveal distinct behaviors and virulence patterns across different host plants. Pcal multiplies to greater levels in cabbage compared to tomato, suggesting that Pcal is more adaptive in cabbage than tomato. Conversely, Pst showed robust multiplication in tomato even at lesser inoculum levels, indicating its aggressiveness in the apoplastic space. Gene expression analyses indicate that these pathogens utilize distinct virulence-related gene expression profiles depending on the host plant. These insights highlight the importance of revealing the spatiotemporal regulation mechanisms of virulence factors. [ABSTRACT FROM AUTHOR]

Pseudomonas cannabina pv. alisalensis (Pcal) causes bacterial blight on cabbage. In a previous study, we screened for reduced virulence using Tn5 transposon mutants and identified a LysR-type transcriptional regulator (LTTR) as a potential virulence factor in Pcal. However, the role of LTTR in Pcal virulence has not been thoroughly investigated. In this study, we demonstrated that the Pcal NN14 mutant (with Tn5 insertion in the LTTR-encoding gene) showed reduced disease symptoms and bacterial populations in cabbage, indicating that LTTR contributes to Pcal virulence. RNA-seq analysis identified 39 LTTR-dependent genes. Genes associated with 13 of the type three secretion system (T3SS), two of flagellar apparatus, ABC transporters, and transcription factors were expressed at lower levels in the NN14 mutant compared to the wild type. Conversely, tssH and hcp, type six secretion system (T6SS)-related genes, showed higher expression in NN14. Furthermore, these differences in gene expression were observed in minimal medium, but not in nutrient-rich medium, suggesting that LTTR acts as a global regulator responsive to nutrient conditions. Additionally, LTTR activated the expression of T3SS-related genes during Pcal infection. We also demonstrated that NN14 showed a reduced ability to induce hypersensitive reaction (HR) cell death in non-host plants. Collectively, these results suggest that LTTR contributes to Pcal virulence by regulating T3SS in response to environmental changes. [ABSTRACT FROM AUTHOR]