Relationship Between Movement And Hypersensitive Response Induction Of Tomato Spotted Wilt Virus

The unique NSm protein of TSWV has typical characteristics of plant viral movement proteins(MPs),including association with and modification of plasmodesmata(Kormelink et al.,1994,Prins et al.,1997,Storms et al.,1998),tubule formation(Storms et al.,1995),RNA binding activity and interaction with N protein(Soellick et al.,2000).The primary function of the NSm protein is to target into plasmodesmata to facilitate cell-to-cell movement of viral ribonucleoproteins(RNPs)or particles.Recently,the NSm protein of TSWV was identified as the avirulence determinant in the Sw-5-mediated hypersensitive response(HR)(Hallwass et al.,2014,Peiro et al.,2014).However whether the primary function of NSm is linked to its function for Sw-5b-mediated HR induction remains unknown.In this study,we demonstrated that NSm mutants that were defective in targeting PD still retain their capability for HR induction.However,introducing the single amino-acid mutations C118Y or T120N,which derive from the resistance-breaking isolate,into the PD-nontargeting mutant of NSm results in the protein no longer inducing HR.Collectively,our results showed that the intercellular trafficking of NSm protein is uncoupled from its HR function.Our findings shed new lights on the evolutionary mechanism of R-Avr recognition which may explain why this uncoupled phenomenon can be observed in many different viruses.