Genômica e evolução de um novo baculovírus isolado da lagarta-praga do trigo Mythimna (Pseudaletia) sequax (Lepidoptera: Noctuidae)

Abstract

Baculoviruses are bioinsecticides widely used in Brazil and in the world and can replace, assist or reduce the consumption of agrochemicals in agricultural crops. They are part of the Baculoviridae family, a family of viruses that contain a double-stranded, supercoiled, circular DNA genome. The genome size varies between 80-180 kb and encodes 90-180 genes, of which only 38 are present in all baculoviruses sequenced to date. They are insect-specific pathogens and are divided into four genera, Alphabaculovirus and Betabaculovirus contain members that are infective for lepidopteran larvae, Gammabaculovirus contain members that are infective for Hymenopteran larvae, and Deltabaculovirus which contain members that are infective for dipteran larvae. In addition, as a distinct characteristic, they present two viral phenotypes during a complete cycle of infection, one responsible for the primary oral infection and which is protected within the body from occlusion, active principle of baculovirus-based bioinsecticides and another phenotype responsible for the spread of secondary infection along the body of the insect. In the present work, the genome of a new baculovirus isolated from the rice and wheat pest of the Mythimna sequax species that causes an economic impact on these crops was characterized. Scanning electron microscopy confirmed the characteristic polyhedral occlusion body of Alphabaculoviruses, hence the virus was named Mythimna sequax nucleopolyhedrovirus (MyseNPV). The virus genome showed 148,403 bp, G + C content of 40.3% and 169 genes were noted, 13 of which are exclusive to this baculovirus. It is a member of the genus Alphabaculovirus and is closely related to seven other baculoviruses that infect insects of the family Noctuidae, including the viruses that infect insects of the genus Mamestra and the species Helicoverpa armigera. Although there are five recognized species among those closely related, only three were true species, MyseNPV being potentially one of them. The other viruses were just viral isolates. This was reinforced by the similarity of the chitinase and cathepsin gene locus between the true species. A selection analysis was performed for each gene shared by all MyseNPV-related genomes using an individual dN/dS analysis. A total of 221 different genes were found with only 152 shared by the eight genomes. Only three genes underwent positive selection in this group, hoar, bro-d and MyseNPV-127. The fp25k, p28, cathepsin, vlf-1 are those that undergo the greatest purification selection of those 152 genes. That said, the increase in the number of fully sequenced baculoviruses is beneficial for a better understanding of baculoviruses and their evolution, potentially helping the use of baculoviruses both as a biopesticide and expression vectors.