Summary• Mosses (Bryophyta) are nonvascular plants that constitute a large part of the photosynthesizing biomass and carbon storage on Earth. Little is known about how this important portion of flora maintains its health status. This study assessed whether the moss, Physcomitrella patens, responds to treatment with chitosan, a fungal cell wall-derived compound inducing defense against fungal pathogens in vascular plants.• Application of chitosan to liquid culture of P. patens caused a rapid increase in peroxidase activity in the medium. For identification of the peroxidase(s), matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF)/MS, other methods and the whole-genome sequence of P. patens were utilized. Peroxidase gene knock-out mutants were made and inoculated with fungi.• The peroxidase activity resulted from a single secreted class III peroxidase (Prx34) which belonged to a P. patens specific phylogenetic cluster in analysis of the 45 putative class III peroxidases of P. patens and those of Arabidopsis and rice. Saprophytic and pathogenic fungi isolated from another moss killed the Prx34 knockout mutants but did not damage wild-type P. patens.• The data point out the first specific host factor that is pivotal for pathogen defense in a nonvascular plant. Furthermore, results provide conclusive evidence that class III peroxidases in plants are needed in defense against hostile invasion by fungi.
The bacteriophage vB_YecM-R1-37 (R1-37) is a lytic yersiniophage that can propagate naturally in different Yersinia species carrying the correct lipopolysaccharide receptor. This large-tailed phage has deoxyuridine (dU) instead of thymidine in its DNA. In this study, we determined the genomic sequence of phage R1-37, mapped parts of the phage transcriptome, characterized the phage particle proteome, and characterized the virion structure by cryo-electron microscopy and image reconstruction. The 262,391-bp genome of R1-37 is one of the largest sequenced phage genomes, and it contains 367 putative open reading frames (ORFs) and 5 tRNA genes. Mass-spectrometric analysis identified 69 phage particle structural proteins with the genes scattered throughout the genome. A total of 269 of the ORFs (73%) lack homologues in sequence databases. Based on terminator and promoter sequences identified from the intergenic regions, the phage genome was predicted to consist of 40 to 60 transcriptional units. Image reconstruction revealed that the R1-37 capsid consists of hexameric capsomers arranged on a T72؍ lattice similar to the bacteriophage KZ. The tail of R1-37 has a contractile sheath. We conclude that phage R1-37 is a representative of a novel phage type that carries the dU-containing genome in a KZ-like head. Bacteriophages, the viruses that infect bacteria, are the most abundant organisms on Earth, and it is estimated that for each microbial isolate at least 10 different phages exist (19,35). Present knowledge indicates that phages are extremely diverse in nature (7a). Studies on bacteriophages have escalated, since they are excellent targets for genomic and evolutionary research and as models for systems biology studies; in addition, they are important vehicles in horizontal gene transfer. Phages are used as tools in bacterial genetics, and phage gene products are used as tools in molecular biology. Furthermore, their potential as therapeutic agents during the increasing emergence of antibiotic resistance is being reexamined (45,46). In summary, a thorough knowledge of the bacteriophage and its biology is considered essential to all phage research.We have isolated several Yersinia enterocolitica-specific bacteriophages that use different parts of lipopolysaccharide (LPS) as receptors and used them to study the molecular biology and genetics of LPS biosynthesis (2,23,24,33,34,(46)(47)(48). The bacteriophage vB_YecM-R1-37 (R1-37) was isolated from sewage based on its ability to infect Y. enterocolitica strain YeO3-R1, an O-polysaccharide (O-PS)-lacking Y. enterocolitica serotype O:3 strain (44, 48). The host range of R1-37, as well as genetic and structural data, showed that the LPS outer core (OC) hexasaccharide of Y. enterocolitica O:3 is the phage receptor (23,37,38,48).Electron microscopy and analysis of its genome indicated that R1-37 is an exceptionally large-tailed phage with an estimated genome size of 270 kb (23). Structural studies on large bacteriophages with contractile tails are currently limited to the Pse...
We have sequenced the genome and identified the structural proteins and lipids of the novel membranecontaining, icosahedral virus P23-77 of Thermus thermophilus. P23-77 has an ϳ17-kb circular double-stranded DNA genome, which was annotated to contain 37 putative genes. Virions were subjected to dissociation analysis, and five protein species were shown to associate with the internal viral membrane, while three were constituents of the protein capsid. Analysis of the bacteriophage genome revealed it to be evolutionarily related to another Thermus phage (IN93), archaeal Halobacterium plasmid (pHH205), a genetic element integrated into Haloarcula genome (designated here as IHP for integrated Haloarcula provirus), and the Haloarcula virus SH1. These genetic elements share two major capsid proteins and a putative packaging ATPase. The ATPase is similar with the ATPases found in the PRD1-type viruses, thus providing an evolutionary link to these viruses and furthering our knowledge on the origin of viruses.
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