Rhabdoviruses are important pathogens of humans, livestock, and plants that are often vectored by insects. Rhabdovirus particles have a characteristic bullet shape with a
lipid envelope and surface-exposed transmembrane
glycoproteins. Sigma virus (SIGMAV) is a member of the Rhabdoviridae and is a naturally occurring disease agent of Drosophila melanogaster. The
infection is maintained in Drosophila populations through vertical transmission via germ cells. We report here the nature of the Drosophila innate immune response to SIGMAV
infection as revealed by quantitative reverse transcription-PCR analysis of differentially expressed genes identified by microarray analysis. We have also compared and contrasted the immune response of the host with respect to two nonenveloped viruses, Drosophila C virus (DCV) and Drosophila X virus (DXV). We determined that SIGMAV
infection upregulates expression of the
peptidoglycan receptor protein genes PGRP-SB1 and PGRP-SD and the
antimicrobial peptide (
AMP) genes Diptericin-A, Attacin-A, Attacin-B, Cecropin-A1, and
Drosocin. SIGMAV
infection did not induce PGRP-SA and the
AMP genes Drosomycin-B, Metchnikowin, and
Defensin that are upregulated in DCV and/or DXV
infections. Expression levels of the Toll and Imd signaling cascade genes are not significantly altered by SIGMAV
infection. These results highlight shared and unique aspects of the Drosophila immune response to the three viruses and may shed light on the nature of the interaction with the host and the evolution of these associations.