Development of immunodiagnostics for the detection of Grapevine leafroll - associated virus 3 (GLRaV-3) in grapevine using in vitro expression and purification of its coat protein gene

A previously cloned coat protein (CP) gene of Grapevine leafroll-associated virus 3 (GLRaV-3) from cultivar Cabernet Souvignon was over-expressed in Escherichia coli strain BL21 expression system as ~ 43 kDa fusion protein containing polyhistidine tag (6His) at its N terminal. The protein was purified from insoluble fraction and reacted positively in western blotting with commercial anti GLRaV-3 polyclonal antiserum (Bioreba, Switzerland) and hence, used as immunogen for the production of polyclonal antisera in New Zealand white rabbits. Polyclonal antiserum specific to GLRaV-3 detected the virus by double antibody sandwich enzyme linked immunosorbent assay using commercial alkaline phosphatase (ALP) conjugated globulin fraction (Bioreba, Switzerland) in GLRaV-3 positive grapevine samples. The immunoreactivity of the antiserum was confirmed through western blotting. The purified antiserum was conjugated with ALP. The primary antiserum along with ALP conjugate successfully detected the GLRaV-3 from the infected sample at 1:8000 and 1:10,000 dilutions, respectively. To the best of our knowledge, it is the first global study wherein the CP of GLRaV-3 was cloned in pET28a(+) expression vector having many advantages over the earlier used expression vectors. The cloned CP gene was expressed, purified and subjected to the production of immunoreagents. The developed immunoreagents will be useful for certification programmes as well as for large scale virus screening to produce GLRaV-3 free grapevines. The indigenously developed immunereagents will provide a cost-effective way of managing grapevine leafroll disease in Indian sub-continent.