Physarum polycephalum is a well-studied microbial eukaryote with unique experimental attributes relative to other experimental model organisms. It has a sophisticated life cycle with several distinct stages including amoebal, flagellated, and plasmodial cells. It is unusual in switching between open and closed mitosis according to specific life-cycle stages. Here we present the analysis of the genome of this enigmatic and important model organism and compare it with closely related species. The genome is littered with simple and complex repeats and the coding regions are frequently interrupted by introns with a mean size of 100 bases. Complemented with extensive transcriptome data, we define approximately 31,000 gene loci, providing unexpected insights into early eukaryote evolution. We describe extensive use of histidine kinase-based two-component systems and tyrosine kinase signaling, the presence of bacterial and plant type photoreceptors (phytochromes, cryptochrome, and phototropin) and of plant-type pentatricopeptide repeat proteins, as well as metabolic pathways, and a cell cycle control system typically found in more complex eukaryotes. Our analysis characterizes P. polycephalum as a prototypical eukaryote with features attributed to the last common ancestor of Amorphea, that is, the Amoebozoa and Opisthokonts. Specifically, the presence of tyrosine kinases in Acanthamoeba and Physarum as representatives of two distantly related subdivisions of Amoebozoa argues against the later emergence of tyrosine kinase signaling in the opisthokont lineage and also against the acquisition by horizontal gene transfer.

There is an urgent need of adjuvants for cutaneous vaccination. Here we report that micro-sterile inflammation induced at inoculation sites can augment immune responses to influenza vaccines in animal models. The inoculation site is briefly illuminated with a handheld, non-ablative fractional laser before the vaccine is intradermally administered, which creates an array of self-healing microthermal zones (MTZs) in the skin. The dying cells in the MTZs send “danger” signals that attract a large number of antigen-presenting cells, in particular, plasmacytoid dendritic cells (pDCs) around each MTZ forming a micro-sterile inflammation array. A pivotal role for pDCs in the adjuvanticity is ascertained by significant abrogation of the immunity after systemic depletion of pDCs, local application of a TNF-α inhibitor, or null mutation of IFN regulatory factor7 (IRF7). In contrast to conventional adjuvants that cause persistent inflammation and skin lesions, micro-sterile inflammation enhances efficacy of influenza vaccines, yet with diminished adverse effects.

Plasmodium formation in the Myxomycete Physarum polycephalum normally involves fusion of haploid amoebae, carrying different alleles at the mating type (mt) locus, to give diploid plasmodia. Strains carrying the mt h allele are capable of undergoing the amoebal-plasmodial transition with high efficiency within amoebal clones, resulting in the formation of haploid plasmodia. NMG mutagenesis of mt h amoebae, followed by an enrichment procedure, was used to isolate mutants in which such clonal plasmodium formation was either delayed or absent. Thirteen mutants of the second type were analysed. Three of these were temperature-sensitive for plasmodium formation. All thirteen mutants were able to form diploid crossed plasmodia when mixed with a mt x strain. Three new genes were identified and designated npfA, npfB and npfC. A mutant allele of npfA rendered clonal plasmodium formation temperature-sensitive, but did not prevent crossing at the non-permissive temperature with derived strains carrying the same mutant allele. No recombination was detected between npfB or npfC and mt, but npfA was unlinked to mt and a locus (apt-1) shown in a previous study to be involved in plasmodium formation. The genes npfB and npfC were distinguished by complementation analysis. Strains of the genotype npfB~; npfC + behaved in the same way as strains carrying the mt 2 allele. The nature of the mutants and the role of the mating-type locus in the initiation of plasmodium formation are discussed.