An Ancestry Perspective of the Evolution of PBS1 Proteins in Plants

The AVRPPHB SUSCEPTIBLE1 (PBS1) and RESISTANCE TO PSEUDOMONAS SYRINGAE 5 (RPS5) proteins are involved in signal transduction to evoke innate plant immune response. In Arabidopsis, PBS1 is cleaved by the AvrPphB (Pseudomonas phaseolicola Avirulence protein B) protease, activating RPS5 and turning in a hypersensitive response (HR). We searched for PBS1 orthologs to trace their origin and evolution. PBS1 orthologs were found in embryophytes and in other plant taxa but with lower similarity. PBS1 phylogenetic analysis indicates high divergence, suggesting that the decoy function described for Arabidopsis PBS1 might be associated with a small fraction of orthologs. Ancestral reconstruction analysis suggests an elevated diversity in the amino acid sequence within the described motifs. All the orthologs contain the conserved PBS1 kinase subdomains, whereas the cleavage motif is present in several embryophyte orthologs but absent in most other taxa. The putative resistance recognition motifs in PBS1 orthologs are highly diverse. PBS1 cleavage site motif is exposed in some 3D structure predictions, whereas it is not in others, suggesting different modes of regulation and functions in PBS1 orthologs. Our findings suggest that PBS1 originated in the lineage that gave rise to embryophytes, with the angiosperm sequences forming a separate clade from pteridophyte proteins.

Humidity Reduces Rapid and Distant Airborne Travel of Viable Viral Particles in Classroom Settings

The transmission of airborne pathogens via aerosols is considered to be the main route through which a number of known and emerging respiratory diseases infect their hosts. It is therefore essential to quantify airborne transmission in closed spaces and determine what recommendations should be implemented to minimize the exposure to the pathogen in built environments. We have developed a method to detect viable virus particles from aerosols by using an aerosolized bacteriophage Phi6 in combination with its host Pseudomonas phaseolicola, which when seeded on agar plates acts as a virus detector that can be placed at a range of distances away from the aerosol-generating source. Based on this method we present two striking results: (1) We consistently detected viable phage particles at distances of 18 feet away from the source within 15-minutes of exposure in a classroom equipped with a state of the art HVAC system. (2) Increasing the relative humidity beyond 40% at a maintained temperature of (22.8 ± 0.2) ° C; significantly reduces the risk of transmission. Our method can be used to quantify the exposure to pathogens at various distances from the source for different amounts of time, data which can be used to set safety standards for room capacity and the efficacy of interventions which aim to reduce pathogen levels in closed spaces of specified size and intended use.

Antimicrobial activities of constituents from isolona cauliflora verdc and cleistochlamys krikii benth, oliv.: Annonaceae

Antimicrobial activities of crude extract, Caulindole D, a mixture of Caulindole E and F, Pinocembrin and an Oxyheptanoid (Clestochlamic acid) from stem bark of Isolona cauliflora and Cleistochlamys krikii on Pseudomonas phaseolicola, Fusarium solani, Botryodiploida theobromae Aspergillus niger and Aspergillus flavus have been investigated. An in vitro bioassay test showed that the crude dichloro-methane extract from C. krikii and a very strong antimicrobial property. The pure compound had strong to moderate inhibitory effect on Pseudomonas syringae pv. phaseolicola and Botryodiplodia theobromae. The pure compounds from Cleistochlamus krikii had more pronounced inhibitory activities than the pure compounds from Isola cauliflora. At lower concentration of 100-200 ppm, the crude extract of Caulindole, mixture of Caulindole E and F, Pinocembrion and Oxyheptanoid had effect on most of the investigated plant pathogens. Higher concentration of 500-1000 ppm had moderate to weak effect on the Aspergillus spp.

Hybrid Frequencies Confirm Limit to Coinfection in the RNA Bacteriophage φ6

ABSTRACT Coinfection of the same host cell by multiple viruses may lead to increased competition for limited cellular resources, thus reducing the fitness of an individual virus. Selection should favor viruses that can limit or prevent coinfection, and it is not surprising that many viruses have evolved mechanisms to do so. Here we explore whether coinfection is limited in the RNA bacteriophage φ6 that infectsPseudomonas phaseolicola. We estimated the limit to coinfection in φ6 by comparing the frequency of hybrids produced by two marked phage strains to that predicted by a mathematical model based on differing limits to coinfection. Our results provide an alternative method for estimating the limit to coinfection and confirm a previous estimate between two to three phages per host cell. In addition, our data reveal that the rate of coinfection at low phage densities may exceed that expected through random Poisson sampling. We discuss whether phage φ6 has evolved an optimal limit that balances the costly and beneficial fitness effects associated with multiple infections.

Sex and the Evolution of Intrahost Competition in RNA Virus φ6

Sex allows beneficial mutations that occur in separate lineages to be fixed in the same genome. For this reason, the Fisher-Muller model predicts that adaptation to the environment is more rapid in a large sexual population than in an equally large asexual population. Sexual reproduction occurs in populations of the RNA virus φ6 when multiple bacteriophages coinfect the same host cell. Here, we tested the model's predictions by determining whether sex favors more rapid adaptation of φ6 to a bacterial host, Pseudomonas phaseolicola. Replicate populations of φ6 were allowed to evolve in either the presence or absence of sex for 250 generations. All experimental populations showed a significant increase in fitness relative to the ancestor, but sex did not increase the rate of adaptation. Rather, we found that the sexual and asexual treatments also differ because intense intrahost competition between viruses occurs during coinfection. Results showed that the derived sexual viruses were selectively favored only when coinfection is common, indicating that within-host competition detracts from the ability of viruses to exploit the host. Thus, sex was not advantageous because the cost created by intrahost competition was too strong. Our findings indicate that high levels of coinfection exceed an optimum where sex may be beneficial to populations of φ6, and suggest that genetic conflicts can evolve in RNA viruses.