In the 50 years since it was first described, Cowpea mosaic virus (CPMV) has become one of the most intensely studied plant viruses. Research in the past 15 to 20 years has shifted from studying the underlying genetics and structure of the virus to focusing on ways in which it can be exploited in biotechnology. This work led first to the use of virus particles to present peptides, then to the creation of a variety of replicating virus vectors and finally to the development of a highly efficient protein expression system that does not require viral replication. The circle has been completed by the use of the latter system to create empty particles for peptide presentation and other novel uses. The history of CPMV in biotechnology can be likened to an Ouroborus, an ancient symbol depicting a snake or dragon swallowing its own tail, thus forming a circle.

Plant viruses are emerging as an attractive alternative to stable genetic transformation for the expression of foreign proteins in plants. The main advantages of using this strategy are that viral genomes are small and easy to manipulate, infection of plants with modified viruses is simpler and quicker than the regeneration of stably transformed plants and the sequence inserted into a virus vector will be highly amplified. One use of these virus expression systems is for vaccine production. Among plant viruses, cowpea mosaic virus makes an ideal candidate for the production of such vaccines because it grows extremely well in host plants, is very stable, and the purification of virus particles, if required, is straightforward. In this article, the authors review the progress made in the development of cowpea mosaic virus-based vectors for vaccine production, making use of two main approaches: epitope presentation and polypeptide expression.

Fusarium oxysporum f. sp. dianthi virus 1 (FodV1) was detected in isolate 116 (116V⁺) of Fusarium oxysporum f. sp. dianthi, reaching such a high accumulation level that it was clearly visible after agarose gel electrophoresis of total DNA extracts. FodV1 consists of four double-stranded RNA segments that correspond to a new mycovirus in the Chrysoviridae family. We obtained an isolate of F. oxysporum f. sp. dianthi 116 (116V⁻) with only a residual level of FodV1 RNA accumulation by single-conidia selection. Compared with 116V⁻, isolate 116V⁺ showed significant phenotypic alterations in vegetative growth and virulence. Thus, the presence of a high titer of mycovirus FodV1 was associated with a modified morphology and a reduced growth of the colonies on solid medium, and with a diminished conidiation in liquid medium. Inoculation of four susceptible carnation cultivars with either 116V⁻ or 116V⁺ showed that the presence of a high titer of FodV1 was also correlated with a significantly reduced virulence of its fungal host. All of the results suggest that FodV1 could be associated with hypovirulence, identifying it as a potential biocontrol agent for Fusarium wilt of carnation. This is the first report of a mycovirus potentially associated with the induction of hypovirulence in the species F. oxysporum.

Mycoviruses appear to be widespread in Fusarium species worldwide. The aim of this work was to identify mycoviral infections in Fusarium spp., isolated from maize and sorghum grown in Argentina, and to estimate their potential effects on the pathogenicity and toxigenesis of the host fungus towards maize. Mycoviruses were identified in 2 out of 105 isolates analyzed; Fusarium verticillioides strain Sec505 and Fusarium andiyazi strain 162. They were characterized as members of the genus Mitovirus by high-throughput sequencing and sequence analysis. The F. verticillioides mitovirus was a novel mycovirus whereas the F. andiyazi mitovirus was found to be a new strain of a previously identified mitovirus. We have named these mitoviruses, Fusarium verticillioides mitovirus 1 (FvMV1) and Fusarium andiyazi mitovirus 1 strain 162 (FaMV1-162). To our knowledge, FvMV1 is the first mycovirus reported as naturally infecting F. verticillioides, the major causal agent of ear rot and fumonisin producer in corn. Both mitoviruses exhibited 100% vertical transmission rate to microconidia. The Fa162 strain infected with FaMV1-162 did not show phenotypic alterations. In contract, F. verticillioides Sec505 infected with FvMV1 showed increased virulence as well as microconidia and fumonisin-B1 production, compared with two uninfected strains. These results suggest that FvMV1 could have a role in modulating F. verticillioides pathogenicity and toxin production worth further exploring.