Recombinant expression of Garlic virus C (GARV-C) capsid protein in insect cells and its potential for the production of specific antibodies

Detecting Tomato Leaf Curl New Delhi Virus Causing Ridge Gourd Yellow Mosaic Disease, and Other Begomoviruses by Antibody-Based Methods

The incidence and severity of begomovirus diseases have been increasing around the world recently, and the ridge gourd [Luffa acutangula (Roxb.) L.] is the latest example of a crop that has become highly susceptible to the outbreak of the tomato leaf curl New Delhi virus (ToLCNDV, genus Begomovirus) in India. Accurate diagnosis of causal agents is important in designing disease management strategies. In this study the coat protein (CP) gene from a ToLCNDV-Rg ridge gourd isolate was used to produce polyclonal antibodies (ToLCNDV-Rg-CP-PAb) in a rabbit. The antibodies successfully detected a 30.5 kDa ToLCNDV-Rg-CP in extracts of symptomatic ridge gourd leaf samples by several assays, such as Western Blotting (WB), Dot Immuno Binding Assay (DIBA), Direct Antigen Coating Enzyme Linked Immuno Sorbent Assay (DAC-ELISA), Immuno Capture Polymerase Chain Reaction (IC-PCR), and Immuno Capture Loop-Mediated Isothermal Amplification (IC-LAMP) assays. However, none of the negative samples tested positive in either of the detection methods. Among all the methods tested, the immunocapture assay, IC-LAMP, was the most sensitive in detecting ToLCNDV-Rg. Furthermore, antibodies generated in this study also detected other commonly occurring begomoviruses in South India, such as tomato leaf curl Palampur virus and squash leaf curl China virus in cucurbits. Together, ToLCNDV-Rg-CP-PAb can be used for detecting at least three species of begomoviruses infecting cucurbits. The obtained antibodies will contribute to monitoring disease outbreaks in multiple crops.

Expression of tomato yellow leaf curl virus coat protein using baculovirus expression system and evaluation of its utility as a viral antigen

DNA encoding the coat protein (CP) of an Egyptian isolate of tomato yellow leaf curl virus (TYLCV) was inserted into the genome of Autographa californica nucleopolyhedrovirus (AcNPV) under the control of polyhedrin promoter. The generated recombinant baculovirus construct harboring the coat protein gene was characterized using PCR analysis. The recombinant coat protein expressed in infected insect cells was used as a coating antigen in an indirect Enzyme-linked immunosorbent assay (ELISA) and dot blot to test its utility for the detection of antibody generated against TYLCV virus particles. The results of ELISA and dot blot showed that the TYLCV-antibodies reacted positively with extracts of infected cells using the recombinant virus as a coating antigen with strong signals as well as the TYLCV infected tomato and beat plant extracts as positive samples. Scanning electron microscope examination showed that the expressed TYLCV coat protein was self-assembled into virus-like particles (VLPs) similar in size and morphology to TYLCV virus particles. These results concluded that, the expressed coat protein of TYLCV using baculovirus vector system is a reliable candidate for generation of anti-CP antibody for inexpensive detection of TYLCV-infected plants using indirect CP-ELISA or dot blot with high specificity.

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.

Molecular variability and genetic structure of the population of Onion yellow dwarf virus infecting garlic in Iran

Onion yellow dwarf virus (OYDV) is one of the most important viral diseases of garlic crops worldwide. This study surveyed the occurrence of OYDV in 26 garlic ecotypes collected from different regions in Iran during 2008-2009. Using an electron microscope, we detected filamentous particles with about 700-800 nm in length and 12 nm in width in five samples. These features are typical of the genus Potyvirus. The coat protein (CP) gene from 26 samples was PCR amplified, cloned, sequenced, and compared with the sequences available in GenBank. Phylogenetic analysis using 235 deduced amino acids of the CP gene showed that virus isolates fell into two groups, group A and group B. Members of group A were divided into two subgroups: A-I and A-II. The subgroup A-I appears to be a new subgroup comprising 17 Iranian isolates. The identity levels among the amino acid of 26 Iranian isolates ranged between 90 and 100%. The results indicated that the genetic diversity found in Iran is due to local OYDV populations rather than introduction from other geographical regions. This study is the first report about the molecular structure and geographically diverse range of OYDV populations in this country.

Characterization of a new Autographa californica multiple nucleopolyhedrovirus (AcMNPV) polyhedra mutant

In the very late phase of baculovirus infection, virions are occluded in a crystalline matrix called polyhedra, which is mainly composed of polyhedrin. This protein is highly conserved among baculoviruses and changes in its amino acid sequence may lead to mutant polyhedra. During the purification of an AcMNPV recombinant virus, a mutant virus was isolated. Structural and ultrastrutural analysis by light and transmission electron microscopy (TEM) of insect cells infected with this mutant virus did not show polyhedra formation and differed from the wild-type infection by the presence of a proteinaceous mass dispersed in the cytoplasm and nucleus of the infected cells, which was confirmed by immunogold labelling to be polyhedrin. The polyhedrin gene was amplified by PCR and sequenced. The only change observed was the substitution of a G to a T at the nucleotide +352, which resulted in a Val to Phe change. A recombinant virus was constructed by transferring the mutant gene into a polyhedrin negative virus. The phenotype of this recombinant virus was the same as the mutant one, confirming that this single mutation alone was responsible for the mutant phenotype.