A naturally occurring mutant of Spodoptera frugiperda multiple nucleopolyhedrovirus reveals the existence of a new alphabaculovirus per os infectivity factor (pif-6)

OIHANE SIMÓN; LEOPOLDO PALMA; TREVOR WILLIAMS; MIGUEL LÓPEZ-FERBER; PRIMITIVO CABALLERO

Congreso; 2011 International Congress on Invertebrate Pathology and Microbial Control & 44th Annual Meeting of the Society for Invertebrate Pathology; 2011

Society for Invertebrate Pathology

The Nicaraguan population of Spodoptera frugiperda multiple nucleopolyhedrovirus, SfMNPV-NIC, is structured as a mixture of genotypes. SfMNPV-C, -D and ?G pure genotypes are incapable of oral transmission. In SfMNPV-C and ?D the non-transmissible phenotype is due to the absence of pif1 and pif2 genes. The complete sequence of the SfMNPV-G genome was determined identify possible factors involved in this phenotype. Two deletions of 4,860 bp (22,364-27,225) and 60 bp (119,759-119,818) were observed in SfMNPV-G genome compared with that of SfMNPV- B, the predominant complete genotype (132,954 bp). However no genes homologous to previously describe per os infectivity factors were detected in these deletions. Significant differences were found in the nucleotide sequence in sf58 gene (unknown function) that produced changes into the amino acid sequence and the predicted secondary structure of the protein. This gene is conserved only in alphabaculoviruses. To determine the role of sf58 in the peroral infectivity a deletion mutant was constructed using bacmid technology. The OBs of the deletion mutant (Sf58null) were not orally infectious for S. frugiperda larvae, although Sf58null DNA and ODVs were as infective as SfMNPV bacmid DNA and ODVs in intrahemocelically infected larvae or cell culture, indicating that defects in ODV or occlusion body morphogenesis were not involved in the observed loss of infectivity. The addition of Tinopal or the presence of the orally infectious SfMNPV-B genotype in mixtures with SfMNPV-G did not recover Sf58null OB infectivity. According to these results sf58 is a new per os infectivity factor (PIF-6) present only in alphabaculoviruses.