A novel approach to virus-induced post-transcriptional gene silencing for studying the function of the ribulose bisphosphate carboxylase small subunlt (rbcS) gene was established and optimized using potato virus X vector and Nicotiana benthamiana as experimental material. The analysis of silencing phenomena,transcriptional level, protein expression, and pigment measurement showed that the expression of the rbcS endogenous gene was inactivated by the expression of a 500-bp homologous cDNA fragment carried in the virus vector.