Characterization of two novel Microplitis demolitor polydnavirus mRNAs expressed in Pseudoplusia includens haemocytes

The braconid wasp Microplitis demolitor carries M. demolitor polydnavirus (MdPDV) and parasitizes the larval stage of the moth Pseudoplusia includens. M. demolitor injects MdPDV into P. includens larvae when it lays an egg and the virus infects various cells including haemocytes. Two new MdPDV transcripts expressed in host haemocytes were characterized in this study. Screening of an MdPDV-infected haemocyte cDNA library identified a 0.4 kb cDNA encoding a predicted protein of 103 amino acids which was named Egf0.4. This protein contained a cysteine-rich epidermal growth factor (EGF)-like motif at its N terminus that was similar to the EGF-like domains in the previously identified MdPDV genes egf1.5 and egf1.0. Sequencing of the genomic clone pMd-10 indicated that it contained the egf0.4 gene, which consisted of two introns and three exons. This gene was located on MdPDV segment O and appeared to exist in multiple copies. A nucleic acid and expression screen identified a 1.8 kb cDNA encoding a predicted protein of 515 amino acids designated Glc1.8. This protein consisted of a heavily glycosylated central core of six tandemly arranged repeats Ranked by hydrophobic N- and C-terminal domains. Northern blotting and in situ hybridization studies indicated that both egf0.4 and glc1.8 were expressed in MdPDV-infected host haemocytes. Immunocytochemical studies also indicated that Glc1.8 localized to the cell surface.