Coat protein 3 of Rice tungro spherical virus is the key target gene for development of RNAi mediated tungro disease resistance in rice

Rice tungro disease (RTD) is the most important viral disease of rice which limits its production and productivity in major rice growing regions of the world. The disease is caused by the combined action of Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV). The RTBV is primarily responsible for symptom development while RTSV encodes proteins required for virus transmission. In this study, we developed an RNAi gene construct containing highly conserved partial sequences of coat protein 3 (CP3) gene of RTSV. The transgenic rice plants were developed in the background of japonica rice cultivar Taipei-309 through Agrobacterium mediated genetic transformation. The transgene showed stable inheritance as determined by PCR and Southern hybridization analyses. Two homozygous transgenic lines from the T₄ generation were inoculated by virus through viruliferous insect vectors. These lines showed highly resistant phenotypes against the tungro disease which was further supported by studies of plant morphology and yield attributes. Also, the transgenic lines showed an inability to transmit the virus complex which could be due to suppression of RTSV proteins involved in virus transmission through insects. This study shows that CP3 of RTSV is a key target gene for development of RNAi mediated tungro disease resistance in rice.