Resistance to Pepper Mild Mottle Tobamovirus Conferred by the 54-kDa Gene Sequence in Transgenic Plants Does Not Require Expression of the Wild-Type 54-kDa Protein

We previously reported thatNicotiana benthamianaplants transformed with the wild-type 54-kDa region of the pepper mild mottle tobamovirus, S strain (PMMoV-S), displayed two different resistance responses against PMMoV infection. Some of the transgenic plants exhibited a complete and highly resistant phenotype while the remaining plants showed a delayed resistance (Tenlladoet al.,1995,Virology211, 170–183). Here we show that some of theN. benthamianaplants transformed with a construct expressing a PMMoV-S truncated 54-kDa protein coding sequence also displayed a complete and highly resistant phenotype similar to that shown by the wild-type 54-kDa transgenic plants. This result indicates that the wild-type, full-length 54-kDa protein is not required in mediating the complete resistance phenotype against PMMoV. The remaining truncated 54-kDa transgenic plants were susceptible to PMMoV infection but showed a variable delay in the appearance of symptoms. Unlike the wild-type 54-kDa transgenic plants, which were initially susceptible to the infection but recovered later, the truncated 54-kDa transgenic plants never exhibited this delayed resistance phenotype. However, they displayed a new type of altered symptomatic phenotype. The truncated 54-kDa transgenic lines also exhibited a lower level of transgenic transcripts compared to the wild-type 54-kDa transgenic lines which could account for the absence of the delayed resistance phenotype.This work was supported by Grants AGF94-0364 and PB94-0023 from the Dirección General de Investigación Científica y Técnica (DGICYT).Peer reviewe