The Physarum polycephalum Genome Reveals Extensive Use of Prokaryotic Two-Component and Metazoan-Type Tyrosine Kinase Signaling

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