Citrus Bright Spot Virus: A New Dichorhavirus, Transmitted by Brevipalpus azores, Causing Citrus Leprosis Disease in Brazil

Abstract

Citrus leprosis (CL) is the main viral disease affecting the Brazilian citriculture. Sweet orange (Citrus sinensis L. Osbeck) trees affected by CL were identified in small orchards in Southern Brazil. Rod-like particles of 40 × 100 nm and electron lucent viroplasm were observed in the nucleus of infected cells in symptomatic tissues. RNA extracts from three plants, which proved negative by RT-PCR for known CL-causing viruses, were analyzed by high throughput sequencing and Sanger sequencing after RT-PCR. The genomes of bi-segmented ss(−)RNA viruses, with ORFs in a typical organization of members of the genus Dichorhavirus, were recovered. These genomes shared 98–99% nt sequence identity among them but <73% with those of known dichorhavirids, a value below the threshold for new species demarcation within that genus. Phylogenetically, the three haplotypes of the new virus called citrus bright spot virus (CiBSV) are clustered with citrus leprosis virus N, which is a dichorhavirus transmitted by Brevipalpus phoenicis sensu stricto. In CiBSV-infected citrus plants, B. papayensis and B. azores were found, but the virus could only be transmitted to Arabidopsis plants by B. azores. The study provides the first evidence of the role of B. azores as a viral vector and supports the assignment of CiBSV to the tentative new species Dichorhavirus australis.

Role of Plant Virus Movement Proteins in Suppression of Host RNAi Defense

“…The OFV-citrus MP has a diffuse cytoplasmic localization and is additionally localized to PD. Importantly, MP associates with structural N and P proteins and directs these proteins from the nucleus to the cell cytoplasm, and subsequently the complex of MP and N (nucleocapsid) proteins is transported to PD [170,171]. The MP is found to be incapable of local silencing suppression of a GFP transgene in a patch agroinfiltration assay or in the TCV movement complementation assay.…”

“…The MP is found to be incapable of local silencing suppression of a GFP transgene in a patch agroinfiltration assay or in the TCV movement complementation assay. However, the OFV-citrus MP inhibits the systemic, but not cell-to-cell, transport of silencing signals (Table 1 and Figure 1) [170][171][172]. The mechanism of silencing suppression by the OFV-citrus MP remains to be elucidated.…”