New tools to study torradovirus molecular biology and epidemiology

Torradoviruses are an emerging group of viruses belonging to the genus Torradovirus, family Secoviridae. Given the growing importance of torradoviruses, it has become essential to provide molecular tools, such as infectious clones, for the establishment of reverse genetic systems to study their life cycles. The first infectious clone for this taxonomic group was for Tomato torrado virus (ToTV), a virus isolated in Spain in 2004. The reverse genetic potential of this infectious clone is currently being exploited. Here, we describe the assembly of an infectious clone of the second characterized torradovirus, tomato apex necrosis virus (ToANV). This virus belongs to the Tomato marchitez virus species and was discovered in 2005 from infections of tomato in Sinaloa, Mexico. This infectious clone can reproduce all the biological properties associated with ToANV, including its ability to be transmitted by its whitefly vector, Bemisia tabaci. Furthermore, we recently characterized a stored virus isolate that was originally collected from open fields in the Lazio region of central Italy in September 2001. This virus isolate caused necrotic tips on tomato 'Nerina'. Electron microscopy and several attempts at virus purification allowed us to establish that no stable virus particle was associated with this isolate. RNA-seq facilitated assembly of the full-length sequence of the viral genome, leading to its classification as an isolate of Tomato torrado virus, therefore antedating its presence in Italy to early 2001. RT-PCR confirmed the presence of this virus in the original sample stored in the PLAVIT collection as lyophilized fruit. We are currently studying the molecular basis of its particle instability.