T sw gene‐based resistance is triggered by a functional RNA silencing suppressor protein of the T omato spotted wilt virus

Summary As a result of contradictory reports, the avirulence ( A vr) determinant that triggers T sw gene‐based resistance in C apsicum annuum against the T omato spotted wilt virus ( TSWV ) is still unresolved. Here, the N and NSs genes of resistance‐inducing ( RI ) and resistance‐breaking ( RB ) isolates were cloned and transiently expressed in resistant C apsicum plants to determine the identity of the A vr protein. It was shown that the NSs RI protein triggered a hypersensitive response ( HR ) in T sw ‐containing C apsicum plants, but not in susceptible C apsicum , whereas no HR was discerned after expression of the N RI / RB protein, or when NSs RB was expressed. Although NSs RI was able to suppress the silencing of a functional green fluorescence protein ( GFP ) construct during A grobacterium tumefaciens transient assays on N icotiana benthamiana , NSs RB had lost this capacity. The observation that RB isolates suppressed local GFP silencing during an infection indicated a recovery of RNA silencing suppressor activity for the NSs protein or the presence of another RNA interference ( RNAi ) suppressor. The role of NSs as RNA silencing suppressor and A vr determinant is discussed in the light of a putative interplay between RNAi and the natural T sw resistance gene.