Purification and characterization of an antiviral protein from prickly pear (Opuntia ficus-indica (L.) Miller) cladode

The infectivity of three RNA plant viruses belonging to the genera Cucumovirus, Potyvirus and Tobamovirus was inhibited by an aqueous extract of prickly pear (Opuntia ficus-indica (L.) Miller) cladode. This antiviral activity was not dialyzable, and not related to isolated plant polysaccharides, but was sensitive to heating and extract treatment with trichloroacetic acid and sodium dodecyl sulfate. An antiviral protein with MW of 28.3 kDa was purified from cactus extract by ammonium sulfate fractionation followed by ion exchange chromatography. The isolated protein inhibited Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus and Tobacco mosaic virus at a concentration of 40 μg mL−1. An IC50 of 2.8 μg mL−1 was calculated for isolated protein for CMV inhibition on faba bean plants. It was demonstrated that the antiviral protein has RNase, but not DNase and protease activity. It interacted with viral nucleic acid in far Western dot blot analysis, was resistant to 2-mercaptoethanol and ethylenediaminetetraacetic acid, and was active in the pH range of 4-10. To our knowledge, this is the first report on inhibitory effect of prickly pear extract on members of Tobamovirus, Potyvirus and Cucumovirus, as well as isolation and characterization of an antiviral protein from prickly pear cladode. This plant can be regarded as an encouraging source of antiviral protein to develop environmentally-friendly compounds for management of plant viral diseases.