A genome-wide association study reveals cytokinin as a major component in the root defense responses against Ralstonia solanacearum.

Bacterial wilt caused by the soil-borne pathogen Ralstonia solancearum is economically devastating, with no effective methods to fight the disease. This pathogen invades plants through their roots and colonizes their xylem, clogging the vasculature and causing rapid wilting. Key to preventing colonization are the early defense responses triggered in the host's root upon infection, which remain mostly unknown. Here, we have taken advantage of a high-throughput in vitro infection system to screen natural variability associated with the root growth inhibition phenotype caused by R. solanacearum in Arabidopsis during the first hours of infection. To analyze the genetic determinants of this trait, we have performed a genome-wide association study, identifying allelic variation at several loci related to cytokinin metabolism, including genes responsible for biosynthesis and degradation of cytokinin. Further, our data clearly demonstrate that cytokinin signaling is induced early during the infection process and cytokinin contributes to immunity against R. solanacearum. This study highlights a new role for cytokinin in root immunity, paving the way for future research that will help in understanding the mechanisms underpinning root defenses.

Type III Secretion-Dependent and -Independent Phenotypes Caused by Ralstonia solanacearum in Arabidopsis Roots.

The causal agent of bacterial wilt, Ralstonia solanacearum, is a soilborne pathogen that invades plants through their roots, traversing many tissue layers until it reaches the xylem, where it multiplies and causes plant collapse. The effects of R. solanacearum infection are devastating, and no effective approach to fight the disease is so far available. The early steps of infection, essential for colonization, as well as the early plant defense responses remain mostly unknown. Here, we have set up a simple, in vitro Arabidopsis thaliana-R. solanacearum pathosystem that has allowed us to identify three clear root phenotypes specifically associated to the early stages of infection: root-growth inhibition, root-hair formation, and root-tip cell death. Using this method, we have been able to differentiate, on Arabidopsis plants, the phenotypes caused by mutants in the key bacterial virulence regulators hrpB and hrpG, which remained indistinguishable using the classical soil-drench inoculation pathogenicity assays. In addition, we have revealed the previously unknown involvement of auxins in the root rearrangements caused by R. solanacearum infection. Our system provides an easy-to-use, high-throughput tool to study R. solanacearum aggressiveness. Furthermore, the observed phenotypes may allow the identification of bacterial virulence determinants and could even be used to screen for novel forms of early plant resistance to bacterial wilt.

Enhancing Localized Pesticide Action through Plant Foliage by Silver-Cellulose Hybrid Patches.

Efficacy and efficiency of pesticide application in the field through the foliage still face many challenges. There exists a mismatch between the hydrophobic character of the leaf and the active molecule, low dispersion of the pesticides on the leaves' surface, runoff loss, and rolling down of the active molecules to the field, decreasing their efficacy and increasing their accumulation to the soil. We produced bacterial cellulose-silver nanoparticles (BC-AgNPs) hybrid patches by in situ thermal reduction under microwave irradiation in a scalable manner and obtaining AgNPs strongly anchored to the BC. Those hybrids increase the interaction of the pesticide (AgNPs) with the foliage and avoids runoff loss and rolling down of the nanoparticles. The positive antibacterial and antifungal properties were assessed in vitro against the bacteria Escherichia coli and two agro-economically relevant pathogens: the bacterium Pseudomonas syringae and the fungus Botrytis cinerea. We showed in vivo inhibition of the infection in Nicotiana benthamiana and tomato leaves, as proven by the suppression of the expression of defense molecular markers and reactive oxygen species production. The hydrogel-like character of the bacterial cellulose matrix increases the adherence to the foliage of the patches.

[Tobacco cessation. Action-stage result as a predictor of successful long-term maintenance]. / Deshabituación tabáquica. Valor del resultado en la fase de acción sobre el resultado en la fase de consolidación.

OBJECTIVE: The paucity of long-term studies makes it difficult to evaluate the sustained abstinence over time of smokers who quit. The objective of the present study was to determine to what extent the results of tobacco cessation interventions are maintained after 5 years. PATIENTS AND METHODS: This was a longitudinal prospective study of 502 smokers. The design was quasi-experimental given that therapy was allocated according to the level of the patients' nicotine dependence: routine minimum intervention for smokers with mild addiction and those not in the preparation stage, and nicotine replacement therapy for patients with moderate-to-high dependence and/or a high level of tobacco consumption. RESULTS: Of the 267 patients followed for 5 years, 29.6% quit and were still abstinent at 1 year, and 18.0% remained abstinent after 5 years. Of those who had managed to stop smoking within 2 months of starting the intervention, 47.4% were still abstinent on follow-up at 5 years while 88.1% of those who failed to quit within 2 months were still smoking 5 years later. CONCLUSIONS: The results observed during the action stage could be of use in reorienting the treatment approach, and a planned schedule of follow-up contacts could help patients maintain the abstinence achieved in the course of the intervention.

Deshabituación tabáquica. Valor del resultado en la fase de acción sobre el resultado en la fase de consolidación / Tobacco cessation: action-stage result as a predictor of successful long-term maintenance

Objetivo: La escasez de estudios a largo plazo dificulta la valoración de la abstinencia mantenida en el tiempo de los fumadores que consiguen dejar de fumar. El objetivo de nuestro estudio ha sido determinar en qué medida los resultados obtenidos tras la intervención para dejar de fumar se consolidan en el tiempo, al cabo de 5 años. Pacientes y métodos: Se ha realizado un estudio longitudinal y prospectivo sobre 502 fumadores, cuasi experimental, al considerar el grado de dependencia nicotínica como criterio para la asignación del tratamiento: intervención mínima sistematizada en los fumadores con dependencia baja o que aún no se encontraban en fase de preparación, y tratamiento sustitutivo con nicotina en aquéllos con dependencia moderada-alta y/o alto consumo de cigarrillos. Resultados: De los 267 pacientes que completaron el seguimiento a los 5 años, el 29,6% dejó de fumar y se mantuvo abstinente al año de seguimiento, y el 18,0% a los 5 años. De los que consiguieron dejar de fumar a los 2 meses de la intervención el 47,4% consolidó su abstinencia al cabo de los 5 años de seguimiento, y de los que no lo consiguieron seguía fumando el 88,1%. Conclusiones: Los resultados observados en la fase de acción pueden considerarse un elemento de ayuda para reorientar la actitud terapéutica, y quizá el planteamiento de controles programados en el tiempo ayude a consolidar la abstinencia tabáquica conseguida durante la intervención

Objective: The paucity of long-term studies makes it difficult to evaluate the sustained abstinence over time of smokers who quit. The objective of the present study was to determine to what extent the results of tobacco cessation interventions are maintained after 5 years. Patients and methods: This was a longitudinal prospective study of 502 smokers. The design was quasi-experimental given that therapy was allocated according to the level of the patients' nicotine dependence: routine minimum intervention for smokers with mild addiction and those not in the preparation stage, and nicotine replacement therapy for patients with moderate-to-high dependence and/or a high level of tobacco consumption. Results: Of the 267 patients followed for 5 years, 29.6% quit and were still abstinent at 1 year, and 18.0% remained abstinent after 5 years. Of those who had managed to stop smoking within 2 months of starting the intervention, 47.4% were still abstinent on follow-up at 5 years while 88.1% of those who failed to quit within 2 months were still smoking 5 years later. Conclusions: The results observed during the action stage could be of use in reorienting the treatment approach, and a planned schedule of follow-up contacts could help patients maintain the abstinence achieved in the course of the intervention