A genome sequence assembly of the phototactic and optogenetic model fungus Blastocladiella emersonii reveals a diversified nucleotide-cyclase repertoire

Abstract The chytrid fungus Blastocladiella emersonii produces spores with swimming tails (zoospores); these cells can sense and swim towards light. Interest in this species stems from ongoing efforts to develop B. emersonii as a model for understanding the evolution of phototaxis and the molecular cell biology of the associated optogenetic circuits. Here we report a highly-contiguous genome assembly and gene annotation of the B. emersonii ATCC 22665 strain. We integrate a PacBio long-read library with an Illumina paired-end genomic sequence survey leading to an assembly of 21 contigs totalling 34.27 Mb. Using these data, we assess the diversity of sensory system encoding genes. These analyses identify a rich complement of G protein-coupled receptors (GPCRs), ion transporters and nucleotide-cyclases, all of which had been diversified by domain recombination and tandem duplication. In many cases these domain combinations have led to the fusion of a protein domain to a transmembrane domain, tying a putative signalling function to the cell membrane. This pattern is consistent with the diversification of the B. emersonii sensory-signalling systems, which likely plays a varied role in the complex lifecycle of this fungus.