The research team, led by Ru Yu and Linshuang Hu of Dezhou University in China, began with the potato cultivar Z1076-1, a variety obtained from a commercial potato industry group. Plants were grown under controlled greenhouse conditions at 26 degrees Celsius with a 16-hour photoperiod and relative humidity between 60 and 70 percent. Seedlings with five to six expanded leaves were inoculated by root drenching with a bacterial suspension of 10 to the sixth colony-forming units per milliliter, while mock-inoculated controls received only the magnesium chloride carrier solution. Disease symptoms were scored daily on a zero-to-five grading scale, from no visible wilting to complete plant mortality, and a Disease Severity Index was calculated from these scores.

To capture the earliest stages of the plant-pathogen encounter, the researchers tracked pathogen proliferation using fliC, a marker gene specific to Ralstonia solanacearum. Quantitative PCR showed that fliC expression rose sharply by two days post-inoculation at the two highest inoculum concentrations, confirming rapid bacterial multiplication. Crucially, the team selected sampling points at one and two days post-inoculation, when bacterial populations had reached high levels but visible necrotic symptoms had not yet developed. This design allowed them to record the plant’s early defense responses before extensive tissue damage confounded the molecular picture.

High-throughput RNA sequencing generated more than 79 million clean reads per library, with quality scores high enough to support confident downstream analysis, and roughly 71 percent of reads mapped to the potato reference genome. The scale of the transcriptional response was striking: comparing infected tissue with mock controls revealed 6,663 differentially expressed genes at one day post-inoculation and 7,390 at two days, with 3,877 genes shared between the two time points. Gene Ontology and KEGG enrichment analyses showed that these genes clustered in pathways governing plant-pathogen interactions, secondary metabolite biosynthesis, and amino acid metabolism, indicating that infection triggers a sweeping reprogramming of redox homeostasis, protein phosphorylation, and immune signaling.

The temporal dynamics of the response told a coherent story. At one day post-inoculation, genes involved in calcium signaling, ethylene response, and oxidative burst were prominently upregulated, including calmodulin-like proteins, calcium-dependent protein kinases, cyclic nucleotide-gated channels, ethylene-responsive transcription factors, the MAP kinase kinase kinase MEKK1, the pathogenesis-related protein PR-1, and the respiratory burst oxidase homolog RBOHB. Meanwhile, jasmonate ZIM-domain repressors, heat shock proteins, and several LRR receptor-like kinases were downregulated. By two days, the upregulated set had expanded to include additional calcium sensors, LysM-containing receptor-like kinases such as CERK1, and WRKY transcription factors, while the jasmonate-related genes continued their decline. The authors interpret this progression as a shift from early pattern-triggered immunity toward later, hormone-mediated effector-triggered defense.

Among the differentially expressed genes, four members of the ERF transcription factor family stood out: StERF80, StERF87, StERF98, and StERF139, all continuously upregulated across both time points. Quantitative PCR validated the sequencing data and revealed important differences in magnitude. StERF139 showed the strongest relative induction, peaking at about 5.8-fold, but its absolute expression was so low that its biological impact was likely limited. StERF87, by contrast, combined a robust 4.7-fold induction with the highest absolute expression level of the group, with FPKM values exceeding 100 at two days post-inoculation. That combination made StERF87 the obvious candidate for functional analysis.

To test its role directly, the team cloned the StERF87 coding sequence into an expression vector under the constitutive 35S promoter and used Agrobacterium-mediated transformation to generate stable transgenic potato lines. Two independent lines, OE#1 and OE#2, showed StERF87 transcript levels approximately 17-fold and 7-fold above wild type, respectively, and western blotting confirmed accumulation of the tagged fusion protein. When four-week-old plants were challenge-inoculated with Ralstonia solanacearum, both overexpression lines displayed substantially enhanced tolerance, with disease severity indices consistently lower than wild type from two through fourteen days post-inoculation. Bacterial titers in the transgenic leaves were significantly reduced at both one and two days. Tuber slice assays told the same story: inoculated tubers from overexpression lines showed only mild browning compared with the severe symptoms of wild type, and bacterial loads in the tuber tissue were significantly lower, with one line showing no measurable increase in pathogen load between three and five days, indicating effective suppression of bacterial growth.

The mechanistic basis of this resistance emerged from a combination of hormone measurements, enzyme assays, and DNA-binding experiments. Overexpression lines maintained higher basal salicylic acid levels and accumulated more than 200 nanograms per gram fresh weight by three days post-inoculation, while ethylene emission in one transgenic line peaked at roughly 620 nanoliters per gram per hour, more than double the wild-type peak. Jasmonic acid, in contrast, remained lower in the transgenic lines, consistent with the well-documented antagonism between salicylic acid and jasmonate signaling. This hormonal reprogramming matters because Ralstonia solanacearum deploys type III effectors specifically to suppress both salicylic acid biosynthesis and ethylene signaling; constitutive activation of these pathways in the transgenic plants likely counteracts that immune suppression. Reactive oxygen species peaked in all genotypes at two days post-inoculation, but the transgenic lines showed a lower peak, and their peroxidase and catalase activities remained consistently higher than wild type at four and six days, suggesting improved ROS scavenging after the defense signal had been delivered.

The decisive molecular evidence came from chromatin immunoprecipitation followed by quantitative PCR and dual-luciferase reporter assays. ChIP-qPCR revealed significant enrichment of StERF87 at a region of the StPR1a promoter containing a GCC-box motif located 300 base pairs upstream of the start codon, but no significant binding to the StPR1b1 promoter or to the promoters of the antioxidant genes StFeSOD3, StPOD3, or StCAT1, implying that regulation of those enzyme genes is indirect. In transient reporter assays in Nicotiana benthamiana, co-expression of StERF87 with a StPR1a promoter-driven luciferase construct produced a strong increase in relative luciferase activity. When the core AGCCGCC motif was mutated to AAAAAAA, that activation was abolished, confirming that the GCC-box is the functional binding site. Yeast assays further established that StERF87 possesses intrinsic transcriptional activation activity. Together, these results demonstrate that StERF87 directly activates StPR1a, a canonical marker of systemic acquired resistance, while the elevated PR1b1 expression in transgenic lines likely follows indirectly from the increased salicylic acid and ethylene levels.

The study positions StERF87 as a hub that integrates direct defense gene activation with hormone reprogramming and redox homeostasis, and the successful generation of bacterial wilt-resistant transgenic potato lines holds clear promise for molecular breeding. The authors caution that their data come from controlled conditions and that multi-year, multi-location field trials will be needed to establish the gene’s practical breeding value. Open questions also remain about the upstream signals that activate StERF87, whether NAC transcription factors regulate it from a higher hierarchical level as has been suggested in banana, and what additional target genes and interacting proteins a genome-wide ChIP-seq analysis might reveal. Even so, the finding that a single ethylene response factor can simultaneously switch on a key resistance marker, tilt the hormonal balance toward defense, and fine-tune antioxidant enzymes marks a significant step toward potatoes that can withstand one of agriculture’s most intractable bacterial enemies.

Subject of Research: StERF87-mediated transcriptional regulation of potato defense responses against the bacterial wilt pathogen Ralstonia solanacearum

Article Title: Transcriptomics and overexpression analyses reveal StERF87 confers resistance to Ralstonia solanacearum in potato

Article References: Yu, R., Gao, M., Cai, L., Wang, S., Chen, Q., Guan, P., Lin, C., Zhang, X., Zheng, S., Jiang, L., Wang, J., & Hu, L. (2026). Transcriptomics and overexpression analyses reveal StERF87 confers resistance to Ralstonia solanacearum in potato. Plant Cell Reports, 45(10), Article 284. https://doi.org/10.1007/s00299-026-03967-7

Image Credits: AI Generated

DOI: 10.1007/s00299-026-03967-7

Keywords: potato, Ralstonia solanacearum, bacterial wilt, StERF87, ERF transcription factors, StPR1a, GCC-box, salicylic acid, ethylene, reactive oxygen species, transcriptomics, plant immunity