Identification, Purification, and Serological Detection of the Major Noncapsid Protein of Rice Grassy Stunt Virus

Abstract

The major noncapsid protein (NCP) of rice grassy stunt virus (RGSV) was detected by sodium dodecyl sulfate polyacrylamide get electrophoresis (SDS-PAGE) and purified by differential pH precipitation and a single ultracentrifugation step. Purified NCP formed needle-shaped crystals at pH 5.0 to 6.0. The NCP is composed of a single protein with a molecular mass of 24 kDa. The yield of NCP was about 20 mg per 100 g of tissue. Because antisera prepared against purified NCP reacted with purified RGSV ribonucleoprotein (RNP) particles, NCP was further purified by SDS-PAGE. The NCP antisera thus obtained reacted strongly and specifically with purified NCP and infected plants in indirect enzyme-linked immunosorbent assay (ELISA). Purified RGSV RNPs and sap from healthy rice (Oryza sativa L.) plants did not elicit a reaction. The RGSV NCP antisera also reacted with the NCP of rice stripe virus. NCP was not detected in insects by these methods, although RGSV was detected in planthoppers by double-antibody sandwich ELISA. Western blot analysis also could detect NCP in extracts of infected plants but not in insects. These results are consistent with those reported for maize stripe virus. RGSV NCP is very similar to the NCP produced by other tenuiviruses.