First Report of Shallot latent virus in Garlic in Brazil

A baculovirus-mediated strategy for full-length plant virus coat protein expression and purification

BACKGROUND

Garlic production is severely affected by virus infection, causing a decrease in productivity and quality. There are no virus-free cultivars and garlic-infecting viruses are difficult to purify, which make specific antibody production very laborious. Since high quality antisera against plant viruses are important tools for serological detection, we have developed a method to express and purify full-length plant virus coat proteins using baculovirus expression system and insects as bioreactors.

RESULTS

In this work, we have fused the full-length coat protein (cp) gene from the Garlic Mite-borne Filamentous Virus (GarMbFV) to the 3'-end of the Polyhedrin (polh) gene of the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). The recombinant baculovirus was amplified in insect cell culture and the virus was used to infect Spodoptera frugiperda larvae. Thus, the recombinant fused protein was easily purified from insect cadavers using sucrose gradient centrifugation and analyzed by Western Blotting. Interestingly, amorphous crystals were produced in the cytoplasm of cells infected with the recombinant virus containing the chimeric-protein gene but not in cells infected with the wild type and recombinant virus containing the hexa histidine tagged Polh. Moreover, the chimeric protein was used to immunize rats and generate antibodies against the target protein. The antiserum produced was able to detect plants infected with GarMbFV, which had been initially confirmed by RT-PCR.

CONCLUSIONS

The expression of a plant virus full-length coat protein fused to the baculovirus Polyhedrin in recombinant baculovirus-infected insects was shown to produce high amounts of the recombinant protein which was easily purified and efficiently used to generate specific antibodies. Therefore, this strategy can potentially be used for the development of plant virus diagnostic kits for those viruses that are difficult to purify, are present in low titers or are present in mix infection in their plant hosts.

Viruses of the genus Allium in the Mediterranean region

Allium species are economically important crops in the Mediterranean basin. Viruses are among the most important pathogens affecting their yield and especially those belonging to the genera Potyvirus, Carlavirus, and Allexivirus. Members of the genus Potyvirus are usually the most abundant and cause most of the damage induced. Nevertheless, coinfections with different viruses are not scarce, especially in garlic, and can have synergistic effects that lead to even greater crop losses. Vegetative propagation of alliums and the transmission of most of their viruses by arthropod vectors have significantly contributed to their wide dissemination in the Mediterranean region and elsewhere in the world. Here, we review the general biological and molecular features, the epidemiology, incidence, and methods of diagnosis of the most widespread allium viruses in the basin. Control measures are proposed depending on the mode of propagation of the various alliums, the epidemiology of their viruses and the cultivation procedures adapted by the Mediterranean farmers. The importance of the production and use of virus-free propagative material in order to combat viral diseases of allium crops is especially highlighted. A final discussion focuses on the main shortages identified in the research area of allium viruses, and proposals are made for putative future developments.