Location: National Germplasm Resources LaboratoryTitle: Identification, transmission and genomic characterization of a new member of the family Caulimoviridae causing a flower distortion disease of Rudbeckia hirta Author
Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2017
Publication Date: 6/2/2017
Citation: Lockhart, B., Mollov, D.S., Olszewski, N., Goldsmith, N. 2017. Identification, transmission and genomic characterization of a new member of the family Caulimoviridae causing a flower distortion disease of Rudbeckia hirta. Virus Research. doi: 10.1016/j.virusres.2017.05.012. Interpretive Summary: Rudbeckia (Black-eyed Susan) is a wildflower used in landscape and natural settings; it is also the Maryland state flower. Distorted flowers were observed on Black-eyed Susans for several years in multiple locations across Minnesota. Such symptoms are usually attributed to a phytoplasma, although none was detected in diseased plants by two different methods. However, a previously undescribed virus was detected in symptomatic plants. This virus was named Rudbeckia flower distortion virus (RuFDV). Transmission studies using both green peach aphids and mechanical inoculation showed that the disease can be transmitted to healthy plants. The complete genomic sequence of this virus was determined. Based on phylogeny and genomic sequence comparisons to known viruses, RuFDV was characterized as a new member of the family Caulimoviridae of DNA viruses. The completion of the RuFDV genome sequence facilitates developing reliable detection methods and better control measures of this newly described virus. This information will be useful to those in the ornamental and landscape plant industry.
Technical Abstract: A disease of Rudbeckia hirta (Black-eyed Susan), characterized by severe flower deformation, was observed in Minnesota during 20010-2016. A previously undescribed virus, named Rudbeckia flower distortion virus (RuFDV), was determined to be the causal agent of the disease. Symptoms induced by RuFDV infection resemble those characteristic of phytoplasma-induced diseases, but no phytoplasmas were detected in RuFDV-infected R. hirta. The virus and the disease were transmitted readily by mechanical inoculation and by the aphid Myzus persicae, but only to R. hirta. Virions of RuFDV are icosahedral, 42-45 nm in diameter, and contain a circular 8222 bp dsDNA genome containing seven open reading frames (ORFs). The ORFs 2-6 have 28-52% amino acid sequence identity to the movement protein (MP), coat protein (CP), aspartic protease (AP), reverse transcriptase (RT) and RNase H, and translational transactivator (TA) domains of known caulimoviruses. The three remaining ORFs (1, 7-8) have no significant amino acid sequence similarity to known viruses. Although the RuFDV ORF 6 is significantly truncated relative to those of other known caulimoviruses, neither this nor the concomitant absence of characteristic virus-encoded cytoplasmic inclusion bodies appears to adversely affect aphid transmission of this virus. Phylogenetic analysis based on the sequence of the RT region revealed no close relationship to known members of the family Caulimoviridae. Based on sequence similarity, genome organization and phylogenetic relatedness, RuFDV appears to be distinct from any currently recognized taxonomic grouping in the family Caulimoviridae.