Sorghum mastrevirus-associated alphasatellites: new geminialphasatellites associated with an African streak mastrevirus infecting wild Poaceae plants on Reunion Island

A new geminialphasatellite associated with wheat dwarf virus identified in winter barley in France

Using a high-throughput sequencing (HTS) approach, we report the discovery of a new alphasatellite identified in a winter barley plant collected in France in 2022 that was also infected by wheat dwarf virus (WDV). The presence of the satellite and of WDV was confirmed by several independent PCR assays, and the complete genome sequence was determined. The circular satellite genome is 1424 nt long and shows typical hallmarks of members of the subfamily Geminialphasatellitinae, including a replication-associated hairpin with a CAGTATTAC sequence and a Rep-encoding open reading frame (ORF). It also possesses a second ORF, embedded in a different frame within the Rep ORF, which is also observed in clecrusatellites and a few other members of the family Alphasatellitidae. Pairwise sequence comparisons and phylogenetic analysis showed that this satellite represents a novel species. Its closest relatives are in the genus Colecusatellite, but it likely represents a new genus given its divergence from other genera of the subfamily Geminialphasatellitinae. Given that WDV was the only virus observed in coinfection with the satellite, the name "wheat dwarf virus-associated alphasatellite" is proposed for this novel agent.

Metagenomics reveals the structure of Mastrevirus-host interaction network within an agro-ecosystem

As highly pervasive parasites that sometimes cause disease, viruses are likely major components of all natural ecosystems. An important step towards both understanding the precise ecological roles of viruses and determining how natural communities of viral species are assembled and evolve is obtaining full descriptions of viral diversity and distributions at ecosystem scales. Here, we focused on obtaining such 'community-scale' data for viruses in a single genus. We chose the genus Mastrevirus (family Geminiviridae), members of which have predominantly been found infecting uncultivated grasses (family Poaceae) throughout the tropical and sub-tropical regions of the world. We sampled over 3 years, 2,884 individual Poaceae plants belonging to thirty different species within a 2-ha plot which included cultivated and uncultivated areas on the island of Reunion. Mastreviruses were found in ∼8 per cent of the samples, of which 96 per cent did not have any discernible disease symptoms. The multitude of host-virus associations that we uncovered reveals both the plant species that most commonly host mastreviruses and the mastrevirus species (such as maize streak virus and maize streak Reunion virus) that have especially large host ranges. Our findings are consistent with the hypothesis that perennial plant species capable of hosting years-long mixed mastrevirus infections likely play a disproportionately important role in the generation of inter-species and inter-strain mastrevirus recombinants.

Complete nucleotide sequence of a begomovirus associated with an alphasatellite and a betasatellite naturally infecting okra in Jordan

The complete nucleotide sequences of a monopartite begomovirus and an associated alphasatellite and betasatellite isolated from naturally infected okra (Abelmoschus esculentus) plants originating from Jordan were determined. The sequences of the begomovirus, alphasatellite, and betasatellites were determined to be 2,764, 1,307, and 1,354 nucleotides in length, respectively. Sequence Demarcation Tool (SDT) and phylogenetic analysis revealed that the begomovirus isolate shared the highest (99.5-99.8%) nt sequence identity with isolates of cotton leaf curl Gezira virus (CLCuGeV), a begomovirus found to exclusively infect cotton in Africa, and recently, in Asia and the Middle East. The DNA sequences of the alphasatellite and betasatellite exhibited the highest nt sequence identity (98.7-98.9% and 92.2-95.3%, respectively) to cotton leaf curl Gezira alphasatellite and cotton leaf curl Gezira betasatellite, respectively. This is the first identification of an African begomovirus, associated with DNA satellites, infecting okra in Jordan.

Requirements for the Packaging of Geminivirus Circular Single-Stranded DNA: Effect of DNA Length and Coat Protein Sequence

Geminivirus particles, consisting of a pair of twinned isometric structures, have one of the most distinctive capsids in the virological world. Until recently, there was little information as to how these structures are generated. To address this, we developed a system to produce capsid structures following the delivery of geminivirus coat protein and replicating circular single-stranded DNA (cssDNA) by the infiltration of gene constructs into plant leaves. The transencapsidation of cssDNA of the Begomovirus genus by coat protein of different geminivirus genera was shown to occur with full-length but not half-length molecules. Double capsid structures, distinct from geminate capsid structures, were also generated in this expression system. By increasing the length of the encapsidated cssDNA, triple geminate capsid structures, consisting of straight, bent and condensed forms were generated. The straight geminate triple structures generated were similar in morphology to those recorded for a potato-infecting virus from Peru. These finding demonstrate that the length of encapsidated DNA controls both the size and stability of geminivirus particles.