Transcriptome of the plant virus vector Graminella nigrifrons, and the molecular interactions of Maize fine streak rhabdovirus transmission

The black-faced leafhopper (Graminella nigrifrons) has been identified as the only known vector for the Maize fine streak virus (MFSV), an emerging plant pathogen in the Rhabdoviridae. Within G. nigrifrons populations, individuals can be experimentally separated into three classes based on their capacity for viral transmission: transmitters, acquirers and non-acquirers. Insect immune response plays an essential role in pathogen defenses. In particular, RNA intereference (RNAi) protects insects from virus infection. Among G. nigrifrons transcriptome database generated by RNA-Seq, 194 ESTs were predicted to be functional in the immune response such as Toll and immune deficiency (IMD) pathways, and 43 ESTs matched to at least one D. melanogaster RNAi/PTGS transcript variant. Transcription profiles of 10 ESTs putatively functioning in immune response were generated among 4 classes of G. nigrifrons by real time quantitative PCR (RT-qPCR). Three out of four genes for peptidoglycan recognition proteins (PGRP - SB1, SD, and LC) and genes for Toll and Spaetzle showed significant down-regulation in MFSV infected G. nigrifrons (transmitters, acquirers and non-acquirers) versus control leafhoppers (raised on healthy plants). However, we did not detect an expression difference of PGRP-LB and Defensin among the 4 classes. Additionally, we observed the significant down-regulation of Ars-2, Dcr-2 and Ago-2 in acquirers and non-acquirers, and a higher level of Ago-2 in transmitters. We hypothesize that gene expression difference among G. nigrifrons was caused by the interactions of G. nigrifrons and MFSV.