Construction and characterization of the infectious cDNA clone of the prevalent Chinese strain SC3 of soybean mosaic virus

The resistance of different soybean varieties to the Chinese isolate SC3 of soybean mosaic virus (SMV) was systematically studied. However, the resistance of different germplasm sources is still poorly understood. We constructed an infectious DNA clone of SMV-SC3 (pSC3) and modified it to allow the expression of yellow fluorescence protein (YFP)/ red fluorescence protein (RFP) during viral infection. By using the infection of pSC3-RFP, we can classify the resistance of different soybean cultivars to SMV-SC3 to the extreme resistance that restricts initial viral replication and the resistance that allows viral replication in the initially inoculated cells but restricts further movement. Also, we tracked the SMV-SC3 infection in susceptible cultivar Nannong 1138-2 (NN1138-2) and found that the seed transmission of SMV to the offspring plants can be tracked and recorded by imaging the virus-driven expression of YFP. Overall, we reveal new aspects of soybean resistance to SMV-SC3 and provide an essential tool to study the infection and transmission of SMV-SC3, which will help decipher the genes involved in SMV pathogenesis and host resistance.