Production of a polyclonal antiserum against recombinant nucleocapsid protein and its application for the detection of fig mosaic virus

In planta expression of specific single chain fragment antibody (scFv) against nucleocapsid protein of fig mosaic virus (FMV)

Fig mosaic virus (FMV) is recognized as the main viral agent associated with the mosaic disease (MD) of fig trees (Ficus carica). Due to its worldwide occurrence, FMV represents the most significant global threat to the production of fig fruit. A disease management strategy against the MD in fig orchards has never been effective; and therefore, expression of recombinant antibody in plant cells could provide an alternative approach to suppress FMV infections. In this study we focused on expressing a specific recombinant antibody, a single-chain variable fragment (scFv), targeting the nucleocapsid protein (NP) of FMV in planta. To accomplish this objective, we inserted the scFv gene into a plant expression vector and conducted transient expression in leaves of Nicotiana tabacum cv. Samson plants. The construct was transiently expressed in tobacco plants by agroinfiltration, and antibody of the anticipated size was detected by immunoblotting. The produced plantibody was then assessed for specificity using ELISA and confirmed by Western blot analysis. In this study, the plantibody developed against FMV could be considered as a potential countermeasure to the infection by conferring resistance to MD.

Developing of specific monoclonal recombinant antibody fused to alkaline phosphatase (AP) for one-step detection of fig mosaic virus

Present study was performed to develop a fusion recombinant monoclonal antibody for one-step and accurate detection of FMV with a specific single-chain variable fragment (scFv) fused to alkaline phosphatase (AP) named as scFv(FMV-NP)-AP. The gene encoding-specific scFv recombinant antibody binding to nucleocapsid protein of Fig Mosaic Virus (FMV-NP) was fused to upstream of AP gene and integrated in pET26b bacterial expression vector. As vector contain pelB signal peptide, the expressed protein is secreted into periplasmic compartment. Recombinant fusion protein was produced in transformed E. coli following induction by IPTG. Extraction and purification of fusion protein was performed under denatured condition. The results of SDS-PAGE and western blot analysis indicated high integrity and purity with a single band protein with expected size of 72 kDa. The total yield of purified scFv(FMV-NP)-AP fusion protein estimated around 0.5-1 mg/l cultured medium. Subsequent colorimetric analysis confirmed presence of alkaline phosphatase activity in prepared scFv-AP fusion protein. Specificity of generated recombinant fusion antibody against cognate antigen and the native virus presented in infected plant extracts was assessed by ELISA, western blot and dot blot assays. Results revealed that scFv(FMV-NP)-AP is able to detect the presence of FMV in infected fig plants. The novel approach, implementing specific recombinant fusion antibody developed in this research, leads to one-step detection of FMV in plants by avoiding the use of chemical enzyme-labeled secondary antibodies.

A Fig Deal: A Global Look at Fig Mosaic Disease and its Putative Associates

Fig mosaic disease (FMD) is a complex viral disease with which 12 viruses, including a confirmed causal agent, fig mosaic emaravirus (FMV), and three viroids are associated worldwide. FMD was first described in California in the early 1930s. Symptoms include foliar chlorosis, deformation, and mosaic patterns. FMD is disseminated by vegetative propagation, seed transmission, and vectors, including a mite, Aceria ficus. Management of the disease in fig orchards relies on scouting and elimination of infected trees. In this review, we focus on the distribution of the FMD-associated viruses and viroids by summarizing worldwide surveys and their genome structure. We also determined the full-length sequence of FMV and fig badnavirus 1 (FBV-1) isolates from Connecticut and compared the virus and viroid sequences from fig isolates. We suggest important areas of research including determining the potential synergistic effect of multiple viruses, elucidating the full-length genome sequence of each associated virus, and relating virus titer to phenotypic changes in Ficus carica.

Development of singleplex and multiplex real-time (Taqman®) RT-PCR assays for the detection of viruses associated with fig mosaic disease

Singleplex and multiplex real-time (TaqMan®) RT-PCR assays were developed to detect seven fig-infecting viruses, i.e., fig leaf mottle-associated virus 1 (FLMaV-1), fig leaf mottle-associated virus 2 (FLMaV-2), fig mild mottle-associated virus (FMMaV), fig mosaic virus (FMV), fig latent virus 1 (FLV-1), fig cryptic virus 1 (FCV-1) and fig fleck-associated virus (FFkaV). The sensitivity of the newly developed TaqMan® assays was compared with the corresponding conventional RT-PCR (RT-PCR) using 10° to 10^-6 serial dilutions of both cDNA and crude fig extracts. The results showed that the Taqman® RT-PCR assays were generally 10² to 10³-fold more sensitive than the RT-PCR assays, except in the case of FLV-1 detection, where the two techniques had the same sensitivity. In the multiplex Taqman® RT-PCR, only a maximum of five viruses could be detected simultaneously in naturally infected fig trees, regardless of which combination of the virus-specific probes and primers were used. Both the RT-PCR and Taqman® RT-PCR assays were used in a large-scale survey of 100 field-grown fig trees in Egypt. The results showed the presence of all seven viruses under study, mostly occurring as mixed infections (63 %). The prevalence of infections observed in the tested samples were as follows: FMV (62 %), FFkaV (59 %), FLMaV-2 (32 %), FLV-1 (16 %), FLMaV-1 (14 %), FCV-1 (7%) and FMMaV (4%). FMV was invariably associated with diseased trees that presented mosaic-like symptoms. In the few cases where the mosaic-affected trees were found to be free of FMV, they were found to be infected with a mixture of two or more other viruses.