First identification and molecular characterization of a novel cherry robigovirus

Complete genome sequence of a novel robigovirus infecting Mentha arvensis

The complete genomic sequence of a novel robigovirus, provisionally named "Mentha arvensis robigovirus 1" (MARV1), was determined by combining next-generation sequencing (NGS), reverse transcription polymerase chain reaction (RT-PCR), and rapid amplification of cDNA ends (RACE) PCR. The complete genomic sequence of this new virus is 7617 nucleotides in length, excluding the 3' poly(A) tail. The MARV1 genome encodes a putative replicase, "triple gene block" proteins, and a coat protein. Phylogenetic analysis demonstrated that MARV1 is a member of the genus Robigovirus, with closest relationships to African oil palm ringspot virus (AOPRV). Furthermore, MARV1-derived small interfering RNAs (siRNAs) showed typical patterns of plant-virus-derived siRNAs produced by the host antiviral RNA interference pathway. This is the first report of a plant virus of the genus Robigovirus in M. arvensis.

Virus classification based on in-depth sequence analyses and development of demarcation criteria using the Betaflexiviridae as a case study

Currently, many viruses are classified based on their genome organization and nucleotide/amino acid sequence identities of their capsid and replication-associated proteins. Although biological traits such as vector specificities and host range are also considered, this later information is scarce for the majority of recently identified viruses, characterized only from genomic sequences. Accordingly, genomic sequences and derived information are being frequently used as the major, if not only, criteria for virus classification and this calls for a full review of the process. Herein, we critically addressed current issues concerning classification of viruses in the family Betaflexiviridae in the era of high-throughput sequencing and propose an updated set of demarcation criteria based on a process involving pairwise identity analyses and phylogenetics. The proposed framework has been designed to solve the majority of current conundrums in taxonomy and to facilitate future virus classification. Finally, the analyses performed herein, alongside the proposed approaches, could be used as a blueprint for virus classification at-large.

Systemic infection and symptom development of agro-inoculated cDNA clone of cherry rusty mottle-associated virus in sweet cherry (Prunus avium)

Cherry rusty mottle-associated virus (CRMaV), which belongs the genus Robigovirus of the family Betaflexiviridae, is strongly associated with cherry rusty mottle disease of sweet cherry, Prunus avium. Here, we report on the successful development of an Agrobacterium-based inoculation system for a cloned CRMaV cDNA construct. Agro-inoculation of virus-free cherry rootstock 'Krymsk6' [P. cerasus x (P. cerasus x P. maackii)] resulted in the development of chlorotic yellow mottle symptoms on systemic leaves beginning at 50 days post inoculation. The presence of CRMaV in 'Krymsk6' agro-inoculated plants was confirmed by RT-PCR and ELISA. Subsequently, CRMaV from agro-inoculated 'Krymsk6' was graft-transmissible onto virus-free sweet cherry rootstock P. avium 'Mazzard' as evidenced by the production of typical cherry rusty mottle symptoms beginning at 35 days post grafting, and further confirmed by western blotting and RT-PCR. These results showed conclusively that CRMaV is the causal agent of cherry rusty mottle disease in sweet cherry. The reverse genetic system presented in this study can be used as a tool to investigate the molecular biology of CRMaV and also a template for infectious clone development for other viruses in the genus Robigovirus.

Discovery and molecular characterization of a novel trichovirus infecting sweet cherry

Contigs with the highest sequence similarity (73%) to Apricot pseudo-chlorotic leaf spot virus (genus Trichovirus, family Betaflexiviridae) were identified by high-throughput sequencing from a symptomless sweet cherry accession. The complete genome sequence of this new virus is 7460 nucleotides, excluding the 3' poly(A) tail. Its genome organization is very similar to several trichoviruses infecting fruit trees, with three open reading frames encoding putative replicase, movement protein and coat protein (CP). The virus shares amino acid sequence identities of 60-73% at replicase and 53-76% at CP with other trichoviruses. Phylogenetic analyses group it and other trichoviruses in a cluster. These results support that this virus, which is tentatively named cherry latent virus 1, should be considered a new member in the genus Trichovirus.