Plant protein phosphatase 2C (PP2C) is recognized as one of the most critical protein family in plants and plays a pivotal role in disease resistance responses. However, the involvement of tomato PP2C family members in resistance to bacterial wilt caused by Ralstonia solanacearum remains poorly understood. In this study, we found that silencing SlPP2C28 increased tomato susceptibility to R. solanacearum; then, we introduced the tomato gene SlPP2C28, which exhibits a strong response to R. solanacearum, into the Nicotiana benthamiana genome via Agrobacterium-mediated transformation, generating high-expression transgenic lines OE-2 and OE-3. Following inoculation with R. solanacearum, the transgenic tobacco plants displayed reduced wilting symptoms, delayed disease onset, lower disease index, reduced stem cross-section damage, decreased internal bacterial colonization, diminished accumulation of reactive oxygen species in leaves, enhanced expression of SlPP2C28, up-regulated expression of defense-related genes NbSOD, NbPOD, and NbPAL along with an increase in the activities of their corresponding enzymes, and elevated expression levels of pathogenesis-related genes NbPR1a, NbPR2, NbPR4, and NbPR10. Collectively, these findings demonstrate that the SlPP2C28 gene has the function of enhancing resistance to bacterial wilt disease.

Tomato bacterial wilt, caused by Ralstonia solanacearum (G⁻), is one of the most devastating plant diseases. Developing effective resistance against this pathogen remains a major challenge in plant disease management. In this study, we constructed a fusion gene BPI-LY by combining the gene encoding the lipophilic functional domains of human bactericidal/permeability-increasing protein (BPI) with the gene of human lysozyme (LY). The recombinant gene BPI-LY was heterologously expressed in yeast and tomato. Preliminary in vitro assays in yeast demonstrated that BPI enhances LY’s antibacterial activity against G⁻ bacteria. Furthermore, overexpression of BPI-LY in tomato delayed onset of the disease in the transgenic lines and lowered the degree of tissue damage and the number of bacteria present in the stems relative to those in the wild-type plant. Additionally, the expression levels of the SlSOD, SlPOD, SlPAL, SlPR5, SlPR10, and SlPR-NP24 genes were indirectly upregulated in the transgenic plants following R. solanacearum inoculation. Collectively, these findings demonstrate that BPI-LY enhances the resistance of transgenic tomato against bacterial wilt caused by R. solanacearum.

The circadian clock genes in tomato are key regulators of cold stress adaptation. However, the low-temperature regulatory mechanism of the circadian clock gene SlPCL1 remains unclear. In this study, we evaluated the role of SlPCL1 in cold tolerance through low-temperature treatment of transgenic plants. Downstream target genes were identified using RNA-seq, RT-qPCR, yeast-one-hybrid (Y1H), dual-luciferase assays, and electrophoretic mobility shift assay (EMSA), while interacting proteins were characterized using yeast-two-hybrid (Y2H), luciferase complementation imaging (LCI), and pull-down assays, thereby elucidating the molecular mechanism underlying SlPCL1-mediated low-temperature regulation. We identified SlPCL1 as a nuclear-localized circadian clock gene with transcriptional repressor activity. Overexpression of SlPCL1 resulted in a cold-sensitive phenotype, whereas virus-induced gene silencing (VIGS)-mediated silencing of SlPCL1 enhanced cold tolerance. SlNPF4.6 functions as an abscisic acid (ABA) transporter involved in ABA transport. RNA-seq and RT-qPCR identified the ABA transporter SlNPF4.6 as a downstream target. Functional assays confirmed that SlPCL1 binds to the MYB element in the SlNPF4.6 promoter to repress its expression. Meanwhile, VIGS-mediated silencing of SlNPF4.6 decreased cold tolerance. Furthermore, the expression levels of the ABA receptor SlPYLs in the silenced lines were significantly reduced, confirming the decrease in intracellular ABA content. SlSUMO1, a ubiquitin-like protein, can influence gene transcription through noncovalent interactions. In addition, SlSUMO1 was found to interact with the SlPCL1 protein, attenuating SlPCL1 transcriptional repression activity. Together, these findings establish an SlSUMO1-mediated fine control mechanism of the SlPCL1-SlNPF4.6 regulatory module. This integration of circadian clock regulation uncovers new molecular mechanisms of cold tolerance and supports the development of cold-resistant breeding materials.

In agricultural production, plants commonly suppress their growth and development under abiotic stresses. We identified the heat shock transcription factor SlHsfC1, and overexpression (OE) lines resulted in a dwarf phenotype. Overexpression lines exhibited reduced cell size and elevated levels of bioactive gibberellins (GAs). However, applying external GA₃ did not restore the dwarf phenotype. Gene expression analysis showed that GA biosynthesis pathway genes (SlKO, SlKAO, SlGA20ox3, and SlGA20ox4) were upregulated, whereas GA metabolic pathway genes (SlGA2ox1 and SlGA2ox2) were downregulated, leading to the accumulation of bioactive gibberellins. However, GA signal transduction pathway genes (SlGAI2 and SlGAI3) were also upregulated, thereby impairing gibberellin signaling in these lines. Protein–DNA interaction assays confirmed that SlHsfC1 directly binds the SlGAI3 promoter and activates its expression. Thus, SlHsfC1 regulates plant height by modulating key genes in the gibberellin signaling pathway.