The Genome of Gryllus bimaculatus Nudivirus Indicates an Ancient Diversification of Baculovirus-Related Nonoccluded Nudiviruses of Insects

Abstract

ABSTRACT The Gryllus bimaculatus nudivirus (GbNV) infects nymphs and adults of the cricket Gryllus bimaculatus (Orthoptera: Gryllidae). GbNV and other nudiviruses such as Heliothis zea nudivirus 1 (HzNV-1) and Oryctes rhinoceros nudivirus (OrNV) were previously called “nonoccluded baculoviruses” as they share some similar structural, genomic, and replication aspects with members of the family Baculoviridae . Their relationships to each other and to baculoviruses are elucidated by the sequence of the complete genome of GbNV, which is 96,944 bp, has an AT content of 72%, and potentially contains 98 predicted protein-coding open reading frames (ORFs). Forty-one ORFs of GbNV share sequence similarities with ORFs found in OrNV, HzNV-1, baculoviruses, and bacteria. Most notably, 15 GbNV ORFs are homologous to the baculovirus core genes, which are associated with transcription ( lef - 8 , lef - 9 , lef - 4 , vlf - 1 , and lef-5 ), replication ( dnapol ), structural proteins ( p74 , pif - 1 , pif - 2 , pif - 3 , vp91 , and odv-e56 ), and proteins of unknown function ( 38K , ac81 , and 19kda ). Homologues to these baculovirus core genes have been predicted in HzNV-1 as well. Six GbNV ORFs are homologous to nonconserved baculovirus genes dnaligase , helicase 2 , rr1 , rr2 , iap - 3 , and desmoplakin . However, the remaining 57 ORFs revealed no homology or poor similarities to the current gene databases. No homologous repeat ( hr ) sequences but fourteen short direct repeat ( dr ) regions were detected in the GbNV genome. Gene content and sequence similarity suggest that the nudiviruses GbNV, HzNV-1, and OrNV form a monophyletic group of nonoccluded double-stranded DNA viruses, which separated from the baculovirus lineage before this radiated into dipteran-, hymenopteran-, and lepidopteran-specific clades of occluded nucleopolyhedroviruses and granuloviruses. The accumulated information on the GbNV genome suggests that nudiviruses form a highly diverse and phylogenetically ancient sister group of the baculoviruses, which have evolved in a variety of highly divergent host orders.