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Plants produce reactive oxygen species (ROS) upon infection, which typically trigger defence mechanisms and impede pathogen proliferation. Root-knot nematodes (RKNs, Meloidogyne spp.) represent highly detrimental pathogens capable of parasitizing a broad spectrum of crops, resulting in substantial annual agricultural losses. The involvement of ROS in RKN parasitism is well acknowledged. In this study, we identified a novel effector from Meloidogyne incognita, named CATLe, that contains a conserved catalase domain, exhibiting potential functions in regulating host ROS levels. Phylogenetic analysis revealed that CATLe is conserved across RKNs. Temporal and spatial expression assays showed that the CATLe gene was specifically up-regulated at the early infection stages and accumulated in the subventral oesophageal gland cells of M. incognita. Immunolocalization demonstrated that CATLe was secreted into the giant cells of the host plant during M. incognita parasitism. Transient expression of CATLe significantly dampened the flg22-induced ROS production in Nicotiana benthamiana. In planta assays confirmed that M. incognita can exploit CATLe to manipulate host ROS levels by directly degrading H2O2. Additionally, interfering with expression of the CATLe gene through double-stranded RNA soaking and host-induced gene silencing significantly attenuated M. incognita parasitism, highlighting the important role of CATLe. Taken together, our results suggest that RKNs can directly degrade ROS products using a functional catalase, thereby manipulating host ROS levels and facilitating parasitism.

Plants produce reactive oxygen species (ROS) upon infection, which typically trigger defence mechanisms and impede pathogen proliferation. Root‐knot nematodes (RKNs, Meloidogyne spp.) represent highly detrimental pathogens capable of parasitizing a broad spectrum of crops, resulting in substantial annual agricultural losses. The involvement of ROS in RKN parasitism is well acknowledged. In this study, we identified a novel effector from Meloidogyne incognita, named CATLe, that contains a conserved catalase domain, exhibiting potential functions in regulating host ROS levels. Phylogenetic analysis revealed that CATLe is conserved across RKNs. Temporal and spatial expression assays showed that the CATLe gene was specifically up‐regulated at the early infection stages and accumulated in the subventral oesophageal gland cells of M. incognita. Immunolocalization demonstrated that CATLe was secreted into the giant cells of the host plant during M. incognita parasitism. Transient expression of CATLe significantly dampened the flg22‐induced ROS production in Nicotiana benthamiana. In planta assays confirmed that M. incognita can exploit CATLe to manipulate host ROS levels by directly degrading H2O2. Additionally, interfering with expression of the CATLe gene through double‐stranded RNA soaking and host‐induced gene silencing significantly attenuated M. incognita parasitism, highlighting the important role of CATLe. Taken together, our results suggest that RKNs can directly degrade ROS products using a functional catalase, thereby manipulating host ROS levels and facilitating parasitism. [ABSTRACT FROM AUTHOR]

Pore-forming toxins (PFTs) are effective tools for pathogens infection. By disrupting epithelial barriers and killing immune cells, PFTs promotes the colonization and reproduction of pathogenic microorganisms in their host. In turn, the host triggers defense responses, such as endocytosis, exocytosis, or autophagy. Bacillus thuringiensis (Bt) bacteria produce PFT, known as crystal proteins (Cry) which damage the intestinal cells of insects or nematodes, eventually killing them. In insects, aminopeptidase N (APN) has been shown to act as an important receptor for Cry toxins. Here, using the nematode Caenorhabditis elegans as model, an extensive screening of APN gene family was performed to analyze the potential role of these proteins in the mode of action of Cry5Ba against the nematode. We found that one APN, MNP-1, participate in the toxin defense response, since the mnp-1(ok2434) mutant showed a Cry5Ba hypersensitive phenotype. Gene expression analysis in mnp-1(ok2434) mutant revealed the involvement of two protease genes, F19C6.4 and R03G8.6, that participate in Cry5Ba degradation. Finally, analysis of the transduction pathway involved in F19C6.4 and R03G8.6 expression revealed that upon Cry5Ba exposure, the worms up regulated both protease genes through the activation of the FOXO transcription factor DAF-16, which was translocated into the nucleus. The nuclear location of DAF-16 was found to be dependent on mnp-1 under Cry5Ba treatment. Our work provides evidence of new host responses against PFTs produced by an enteric pathogenic bacterium, resulting in activation of host intestinal proteases that degrade the PFT in the intestine. Author summary: Pore-forming toxins (PFTs) have a crucial role in the pathogenesis of microbial pathogens. Meanwhile, hosts mediate different strategies to resist PFTs at the cellular level, such as endocytosis, exocytosis, autophagy, and MAPK or inflammasome signaling pathways. Here we show that the nematode Caenorhabditis elegans respond to PFTs inducing their proteolysis by up regulating intestinal proteases through the induction of FOXO transcription factor DAF-16 that showed nuclear location. Our results indicate that animals not only trigger defense mechanisms after PFTs intoxication at the cellular level, but also could eliminate PFTs in the intestine lumen, an effective additional strategy for animals to resist PFTs, especially those produced by enteric bacterial pathogens. Since, the FOXO transcription factor DAF-16 is conserved from nematodes to mammals, it is possible that the degradation of PFT by modulating intestinal proteases may be a common defense strategy against bacterial infections. [ABSTRACT FROM AUTHOR]