Crystal Structure-Based Exploration of Arginine-Containing Peptide Binding in the ADP-Ribosyltransferase Domain of the Type III Effector XopAI Protein

Delivery of Apoplastic Extracellular Vesicles Encapsulating Green-Synthesized Silver Nanoparticles to Treat Citrus Canker

The citrus canker pathogen Xanthomonas axonopodis has caused severe damage to citrus crops worldwide, resulting in significant economic losses for the citrus industry. To address this, a green synthesis method was used to develop silver nanoparticles with the leaf extract of Phyllanthus niruri (GS-AgNP-LEPN). This method replaces the need for toxic reagents, as the LEPN acts as a reducing and capping agent. To further enhance their effectiveness, the GS-AgNP-LEPN were encapsulated in extracellular vesicles (EVs), nanovesicles with a diameter of approximately 30-1000 nm naturally released from different sources, including plant and mammalian cells, and found in the apoplastic fluid (APF) of leaves. When compared to a regular antibiotic (ampicillin), the delivery of APF-EV-GS-AgNP-LEPN and GS-AgNP-LEPN to X. axonopodis pv. was shown to have more significant antimicrobial activity. Our analysis showed the presence of phyllanthin and nirurinetin in the LEPN and found evidence that both could be responsible for antimicrobial activity against X. axonopodis pv. Ferredoxin-NADP⁺ reductase (FAD-FNR) and the effector protein XopAI play a crucial role in the survival and virulence of X. axonopodis pv. Our molecular docking studies showed that nirurinetin could bind to FAD-FNR and XopAI with high binding energies (-10.32 kcal/mol and -6.13 kcal/mol, respectively) as compared to phyllanthin (-6.42 kcal/mol and -2.93 kcal/mol, respectively), which was also supported by the western blot experiment. We conclude that (a) the hybrid of APF-EV and GS-NP could be an effective treatment for citrus canker, and (b) it works via the nirurinetin-dependent inhibition of FAD-FNR and XopAI in X. axonopodis pv.

The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years

The Physical Chemistry and Chemical Physics Section (PCCP Section) is one of the youngest among the sections of the International Journal of Molecular Sciences (IJMS)—the year 2021 will only mark three years since its inception [...]

What the Wild Things Do: Mechanisms of Plant Host Manipulation by Bacterial Type III-Secreted Effector Proteins

Phytopathogenic bacteria possess an arsenal of effector proteins that enable them to subvert host recognition and manipulate the host to promote pathogen fitness. The type III secretion system (T3SS) delivers type III-secreted effector proteins (T3SEs) from bacterial pathogens such as Pseudomonas syringae, Ralstonia solanacearum, and various Xanthomonas species. These T3SEs interact with and modify a range of intracellular host targets to alter their activity and thereby attenuate host immune signaling. Pathogens have evolved T3SEs with diverse biochemical activities, which can be difficult to predict in the absence of structural data. Interestingly, several T3SEs are activated following injection into the host cell. Here, we review T3SEs with documented enzymatic activities, as well as T3SEs that facilitate virulence-promoting processes either indirectly or through non-enzymatic mechanisms. We discuss the mechanisms by which T3SEs are activated in the cell, as well as how T3SEs modify host targets to promote virulence or trigger immunity. These mechanisms may suggest common enzymatic activities and convergent targets that could be manipulated to protect crop plants from infection.

Exploring folds, evolution and host interactions: understanding effector structure/function in disease and immunity

Over the past decade, tremendous progress has been made in plant pathology, broadening our understanding of how pathogens colonize their hosts. To manipulate host cell physiology and subvert plant immune responses, pathogens secrete an array of effector proteins. A co-evolutionary arms-race drives the pathogen to constantly reinvent its effector repertoire to undermine plant immunity. In turn, hosts develop novel immune receptors to maintain effector recognition and mount defences. Understanding how effectors promote disease and how they are perceived by the plant's defence network persist as major subjects in the study of plant-pathogen interactions. Here, we focus on recent advances (over roughly the last two years) in understanding structure/function relationships in effectors from bacteria and filamentous plant pathogens. Structure/function studies of bacterial effectors frequently uncover diverse catalytic activities, while structure-informed similarity searches have enabled cataloguing of filamentous pathogen effectors. We also suggest how such advances have informed the study of plant-pathogen interactions.