Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/9/2004
Publication Date: 5/1/2005
Citation: Tsai, C., Redinbaugh, M.G., Willie, K.J., Reed, S.E., Goodwin, M., Hogenhout, S.A. 2005. Sequence and functional analysis of the maize fine streak virus (mfsv) genome. Phytopathology. 94:S103. Interpretive Summary: Maize fine streak virus (MFSV) is a newly discovered leafhopper transmitted rhabdovirus that infects maize. Little was known about the genomic sequence or structure of this virus. We showed that the MFSV genome carries 7 genes that are all expressed in infected plants. We could assign functions for 5 of the 7 genes based on comparisons with related viruses, and on the structure and subcellular distribution of the gene-encoded proteins. Researchers will use this information for projects to identify virus factors that determine insect and plant host range, comparative studies of rhabdoviruses and development of viral vectors with reduced tendencies for recombination.
Technical Abstract: The genome of the nucleorhabdovirus maize fine streak virus (MFSV) consists of 13,782 nucleotides of nonsegmented, negative-sense, single-stranded RNA. Seven open reading frames (ORFs) were identified on the anti-genomic strand and transcripts to all of these ORFs were detected in infected plants. ORF1, ORF6, and ORF7 had significant similarities to the nucleocapsid protein (N), glycoprotein (G), and polymerase (L) genes of other rhabdoviruses, respectively. In contrast, the ORF2, ORF3, ORF4, and ORF5 proteins had no significant similarities to sequences in GenBank. When transiently expressed in plant cells, the N (ORF1), ORF4, and ORF5 proteins localized to nuclei consistent with presence of nuclear localization signals (NLSs) in these proteins. ORF5 likely encodes the matrix protein (M) based on its size, position of its NLS, and localization of fluorescent protein fusions to the nucleus. ORF2 probably encodes the phosphoprotein (P) because similar to the P protein of Sonchus yellow net virus (SYNV), it was spread throughout the cell when expressed alone but was relocalized to a subnuclear locus when coexpressed with the MFSV N protein. Coexpression of the MFSV N and P proteins, but not the orthologous proteins of SYNV, resulted in accumulations of both proteins in the nucleolus. Reciprocal expression studies showed that the N and P proteins relocalization was specific to cognate proteins of each virus. Finally, subcellular localizations of the MFSV ORF3 and ORF4 proteins were distinct from that of the SYNV sc4 protein suggesting different functions. IMPACT STATEMENT: This work will directly impact research projects to identify virus factors that determine insect and plant host range, comparative studies of rhabdoviruses and the development of viral vectors with reduced tendencies for recombination. Transmission of maize-infecting rhabdoviruses by their insect vectors is highly species specific, and nothing is known about molecular factors that govern the virus' ability to infect insects. The information provided in this report provides the basis for developing and testing hypotheses about the role of specific virus genes in insect transmission. This report also provides information for researchers interested in studying the comparative genomic structures and sequences of the family Rhabdoviridae, a group of viruses that contains important human, livestock and crop pathogens. Recently a number of viruses have been developed as vectors for expression and/or silencing of host plant genes. However, sequences inserted into most of these vectors are easily deleted through recombination in the plant. It is thought that vectors based on viruses for which the genomic RNA is non-coding (i.e., negative sense RNA viruses) will be more stable in planta. The genome sequence information provided is critical to the development of a vector based on Maize fine streak virus. The work should have moderate to high scientific impact.