Signatures of transposon-mediated genome inflation, host specialization, and photoentrainment inEntomophthora muscaeand allied entomophthoralean fungi

Abstract

AbstractDespite over a century of observations, the obligate insect parasites within the order Entomophthorales remain poorly characterized at the genetic level. This is in part due to their large genome sizes and difficulty in obtaining sequenceable material. In this manuscript, we leveraged a recently-isolated, laboratory-tractableEntomophthora muscaeisolate and improved long-read sequencing to obtain a largely-complete entomophthoralean genome. OurE. muscaeassembly is 1.03 Gb, consists of 7,810 contigs and contains 81.3% complete fungal BUSCOs. Using a comparative approach with other available (transcriptomic and genomic) datasets from entomophthoralean fungi, we provide new insight into the biology of these understudied pathogens. We offer a head-to-head comparison of morphological and molecular data for species within theE. muscaespecies complex. Our findings suggest that substantial taxonomic revision is needed to define species within this group and we provide recommendations for differentiating strains and species in the context of the existing body ofE. muscaescientific literature. We show that giant genomes are the norm within Entomophthoraceae owing to extensive, but not recent, Ty3 retrotransposon activity, despite the presence of anti-transposable element defense machinery (RNAi). In addition, we find thatE. muscaeand its closest allies are enriched for M16A peptidases and possess genes that are likely homologs to the blue-light sensorwhite-collar 1, aNeurospora crassagene that has a well-established role in maintaining circadian rhythms. We find thatE. muscaehas an expanded group of acid-trehalases, consistent with trehalose being the primary sugar component of fly (and insect) hemolymph. We uncover evidence thatE. muscaediverged from other entomophthoralean fungi by expansion of existing families, rather than loss of particular domains, and possesses a potentially unique suite of secreted catabolic enzymes, consistent withE. muscae’s species-specific, biotrophic lifestyle. Altogether, we provide a genetic and molecular foundation that we hope will provide a platform for the continued study of the unique biology of entomophthoralean fungi.