Heat-induced SUMOylation differentially affects bacterial effectors in plant cells.

Bacterial pathogens deliver effectors into host cells to suppress immunity. How host cells target these effectors is critical in pathogen-host interactions. SUMOylation, an important type of posttranslational modification in eukaryotic cells, plays a critical role in immunity, but its effect on bacterial effectors remains unclear in plant cells. In this study, using bioinformatic and biochemical approaches, we found that at least 16 effectors from the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 are SUMOylated by the enzyme cascade from Arabidopsis thaliana. Mutation of SUMOylation sites on the effector HopB1 enhances its function in the induction of plant cell death via stability attenuation of a plant receptor kinase BRASSINOSTEROID INSENSITIVE 1 (BRI1)-ASSOCIATED RECEPTOR KINASE 1. By contrast, SUMOylation is essential for the function of another effector, HopG1, in the inhibition of mitochondria activity and jasmonic acid signaling. SUMOylation of both HopB1 and HopG1 is increased by heat treatment, and this modification modulates the functions of these 2 effectors in different ways in the regulation of plant survival rates, gene expression, and bacterial infection under high temperatures. Therefore, the current work on the SUMOylation of effectors in plant cells improves our understanding of the function of dynamic protein modifications in plant-pathogen interactions in response to environmental conditions.

Sensitivity Variations in Developmental Toxicity of Imidacloprid to Zebrafish Embryos at Different Neurodevelopmental Stages.

Neonicotinoids are ubiquitous in global surface waters and pose a significant risk to aquatic organisms. However, information is lacking on the variations in sensitivity of organisms at different developmental stages to the neurotoxic neonicotinoids. We established a spectrum of toxicity to zebrafish embryos at four neurodevelopmental stages (1, 3, 6, and 8 h post fertilization [hpf]) and dechorionated embryos at 6 hpf based on external and internal exposure to imidacloprid as a representative neonicotinoid. Embryos at the gastrula stage (6 and 8 hpf) were more sensitive to imidacloprid than embryos at earlier developmental stages. Dechorionated embryos were more sensitive to imidacloprid than embryos with a chorion, suggesting that the chorion offers protection against pollutants. Nine sublethal effects were induced by imidacloprid exposure, among which uninflated swim bladder (USB) was the most sensitive. Water depth and air availability in the exposure chambers were critical factors influencing the occurrence of USB in zebrafish larvae. Internal residues of metabolites accounted for <10% of imidacloprid, indicating that imidacloprid was metabolized in a limited fashion in the embryos. In addition, acute toxicity of the main metabolite 5-hydroxy-imidacloprid was significantly lower than that of imidacloprid, indicating that the observed toxicity in embryos exposed to imidacloprid was mainly induced by the parent compound. Our research offers a fresh perspective on choosing the initial exposure time in zebrafish embryo toxicity tests, particularly for neurotoxicants. Environ Toxicol Chem 2024;00:1-11. © 2024 SETAC.