RT Journal Article SR Electronic(1) A1 Chen, Longxin A1 Gao, Xingke A1 Li, Runting A1 Zhang, Limeng A1 Huang, Rui A1 Wang, Linqing A1 Song, Yue A1 Xing, Zhenzhen A1 Liu, Ting A1 Nie, Xiaoning A1 Nie, Fangyuan A1 Hua, Shuang A1 Zhang, Zihan A1 Wang, Feng A1 Ma, Runlin Z. A1 Zhang, LongYR 2020 T1 Complete genome of a unicellular parasite (Antonospora locustae) and transcriptional interactions with its host locust JF Microbial Genomics, VO 6 IS 9 OP SP e000421 DO https://doi.org/10.1099/mgen.0.000421 PB Microbiology Society, SN 2057-5858, AB Microsporidia are a large group of unicellular parasites that infect insects and mammals. The simpler life cycle of microsporidia in insects provides a model system for understanding their evolution and molecular interactions with their hosts. However, no complete genome is available for insect-parasitic microsporidian species. The complete genome of Antonospora locustae, a microsporidian parasite that obligately infects insects, is reported here. The genome size of A. locustae is 3 170 203 nucleotides, composed of 17 chromosomes onto which a total of 1857 annotated genes have been mapped and detailed. A unique feature of the A. locustae genome is the presence of an ultra-low GC region of approximately 25 kb on 16 of the 17 chromosomes, in which the average GC content is only 20 %. Transcription profiling indicated that the ultra-low GC region of the parasite could be associated with differential regulation of host defences in the fat body to promote the parasite’s survival and propagation. Phylogenetic gene analysis showed that A. locustae, and the microsporidian family in general, is likely at an evolutionarily transitional position between prokaryotes and eukaryotes, and that it evolved independently. Transcriptomic analysis showed that A. locustae can systematically inhibit the locust phenoloxidase PPO, TCA and glyoxylate cycles, and PPAR pathways to escape melanization, and can activate host energy transfer pathways to support its reproduction in the fat body, which is an insect energy-producing organ. Our study provides a platform and model for studies of the molecular mechanisms of microsporidium–host interactions in an energy-producing organ and for understanding the evolution of microsporidia., UL https://www.microbiologyresearch.org/content/journal/mgen/10.1099/mgen.0.000421