For most Gram-negative bacteria, pathogenicity largely depends on the type-III secretion system that delivers virulence effectors into eukaryotic host cells. The subcellular targets for the majority of these effectors remain unknown. Xanthomonas campestris, the causal agent of black rot disease of crucifers such as Brassica spp., radish, and turnip, delivers XopP, a highly conserved core-effector protein produced by X. campestris, which is essential for virulence. Here, we show that XopP inhibits the function of the host–plant exocyst complex by direct targeting of Exo70B, a subunit of the exocyst complex, which plays a significant role in plant immunity. XopP interferes with exocyst-dependent exocytosis and can do this without activating a plant NOD-like receptor that guards Exo70B in Arabidopsis. In this way, Xanthomonas efficiently inhibits the host’s pathogen-associated molecular pattern (PAMP)-triggered immunity by blocking exocytosis of pathogenesis-related protein-1A, callose deposition, and localization of the FLAGELLIN SENSITIVE2 (FLS2) immune receptor to the plasma membrane, thus promoting successful infection. Inhibition of exocyst function without activating the related defenses represents an effective virulence strategy, indicating the ability of pathogens to adapt to host defenses by avoiding host immunity responses.

The wide host range of Xylella fastidiosa (Xf) indicates the existence of yet uncharacterized virulence mechanisms that help pathogens to overcome host defences. Various bioinformatics tools combined with prediction of the functions of putative virulence proteins are valuable approaches to study microbial pathogenicity. We collected a number of putative effectors from three Xf strains belonging to different subspecies: Temecula‐1 (subsp. fastidiosa), CoDiRO (subsp. pauca), and Ann‐1 (subsp. sandyi). We designed an in planta Agrobacterium‐based expression system that drives the expressed proteins to the cell apoplast, in order to investigate their ability to activate defence in Nicotiana model plants. Multiple Xf proteins differentially elicited cell death‐like phenotypes in different Nicotiana species. These proteins are members of different enzymatic groups: (a) hydrolases/hydrolase inhibitors, (b) serine proteases, and (c) metal transferases. We also classified the Xf proteins according to their sequential and structural similarities via the I‐TASSER online tool. Interestingly, we identified similar proteins that were able to differentially elicit cell death in different cultivars of the same species. Our findings provide a basis for further studies on the mechanisms that underlie both defence activation in Xf resistant hosts and pathogen adaptation in susceptible hosts.

Plant immunity relies on cell-surface receptors and intracellular NLR immune receptors. Some plant NLRs carry integrated domains (IDs) that that mimic authentic pathogens effector targets. We report here the identification in Brassica napus of the genetically linked NLR/NLR-ID pair, Bn RPR1 and Bn RPR2. The NLR-ID carries two ID fusions and their mode of action conforms to the proposed “integrated sensor/decoy” model. The two NLRs interact and the heterocomplex localizes in the plant-cell nucleus and nucleolus. However, the Bn RPRs pair does not operate through a negative regulation as it was previously reported for other NLR-IDs. Cell death is induced only upon co-expression of the two proteins and it is dependent on the helper genes EDS1 and NRG1. Truncations of the IDs of Bn RPR1 results in cytoplasmic localization and compromises cell death activation. Expression, using the native promoter in Nicotiana species, led to a conditional cell death induction. However, this was not the case for the transgenic Arabidopsis, where no cell death was observed. In summary, we describe a new pair of NLR-IDs with interesting features in relation to its regulation and the cell death activation.

Point-of-care diagnostics are revolutionizing the detection of plant pathogens by enabling rapid, on-site identification without the need for specialized laboratories. One of the tools used for this purpose is loop-mediated isothermal amplification (LAMP). LAMP is a powerful molecular technique increasingly used in pathogen control for its rapid, sensitive, and specific detection of plant pathogens. The aim of this study was the development of a novel, easy-to-use portable colorimetric LAMP (cLAMP) assay that could be used by inexperienced personnel for the detection of the pathogen Clavibacter michiganensis. The assay was combined with a newly constructed device in which LAMP can be performed in 30 min. Initially, a new set of LAMP primers targeting the micA gene was designed and evaluated the sensitivity (100 fg/reaction) and specificity of the assay. Next, the limit of detection (LoD) of two different commercial LAMP kits was compared with common laboratory detection techniques (DAS-ELISA, immunofluorescence, quantitative PCR, and PCR) using the same samples. Additionally, the LoD of the developed cLAMP assay was evaluated in bacterial suspensions and plant extracts spiked with C. michiganensis and validated the effect on the LoD of plant extracts from different tomato varieties. Lastly, its efficacy for C. michiganensis detection was assessed in experimentally inoculated tomato seedlings. The developed method for C. michiganensis detection can be used as a reliable tool for the early detection of the pathogen for field-based applications by untrained personnel.

Hydroxytyrosol (HT) is a phenolic substance primarily present in olive leaves and olive oil. Numerous studies have shown its advantages for human health, making HT a potentially active natural component with significant added value. Determining strategies for its low-cost manufacturing by metabolic engineering in microbial factories is hence still of interest. The objective of our study was to assess and improve HT production in a one-liter bioreactor utilizing genetically modified Escherichia coli strains that had previously undergone fed-batch testing. Firstly, we compared the induction temperatures in small-scale whole-cell biocatalysis studies and then examined the optimal temperature in a large volume bioreactor. By lowering the induction temperature, we were able to double the yield of HT produced thereby, reaching 82% when utilizing tyrosine or L-DOPA as substrates. Hence, without the need to further modify our original strains, we were able to increase the HT yield.

Resveratrol, a polyphenolic stilbene phytoalexin found in high concentrations in red grape skins ( Vitis vinifera ), was evaluated for antimicrobial efficacy against key plant‐pathogenic bacteria and fungi through both in vitro and in planta assays, while exploring its role in modulating plant basal immunity. In vitro growth kinetics demonstrated a clear dose‐dependent inhibition of four major bacterial pathogens: Pseudomonas syringae pv. tomato , Xanthomonas campestris pv. campestris , Acidovorax citrulli and Clavibacter michiganensis . Complete growth arrest for all tested species was achieved at a concentration of 100 μg/mL. Time‐killing assays revealed that resveratrol's activity is primarily bacteriostatic rather than bactericidal, an attribute that may limit the selective pressure for the development of pathogen resistance. Regarding antifungal activity, resveratrol significantly inhibited the mycelial growth of Fusarium oxysporum f. sp. radicis‐cucumerinum and Alternaria alternata . However, Botrytis cinerea exhibited notable tolerance, probably due to its specialized ability to enzymatically degrade or metabolize stilbene compounds. In planta experiments with Arabidopsis thaliana plants showed that foliar pretreatment with resveratrol significantly reduced the proliferation of P. syringae pv. tomato . Molecular analysis via reverse transcription‐quantitative PCR provided evidence of immune ‘priming’ as resveratrol induced the expression of pattern‐triggered immunity marker genes. This research highlights the dual functionality of resveratrol as both a direct antimicrobial agent and a potent inducer of plant defence responses. These findings position resveratrol as a viable, eco‐friendly tool for integrated disease management, although further studies on field stability and bioavailability are required for practical agricultural implementation.