NICOTIANA-BENTHAMIANA PLANTS TRANSFORMED WITH THE 54-KDA REGION OF THE PEPPER MILD MOTTLE TOBAMOVIRUS REPLICASE GENE EXHIBIT 2 TYPES OF RESISTANCE RESPONSES AGAINST VIRAL-INFECTION

Nicotiana benthamiana plants transformed with the 54-kDa region of the pepper mild mottle tobamovirus (PMMV) replicase gene were generated a nd six independently transformed plant lines were analyzed for resista nce to PMMV. Two different resistance responses were obtained. Some of the transgenic plants from only two lines showed a preestablished, co mplete, and highly resistant phonotype since no viral symptoms were ob served, although a low level of virus replication occurred. The remain ing plants from these two lines and all of the plants from the other f our lines tested showed a delayed, induced, and also highly resistant phenotype since they were susceptible early, but were able to recover from the systemic PMMV infection. Recovered, symptomless leaves were r esistant to the PMMV strain from which the 54-kDa gene was derived and to a closely related strain but not to tobacco mosaic virus. Such a d elayed resistance phenotype has not been previously described for any plant expressing viral replicase sequences. The transgenic plants with in the lines displaying complete or delayed resistance phenotypes were analyzed for transgene expression before and after PMMV inoculation a nd the two types of resistance responses were shown to be independent of the transgene transcript level. (C) 1995 Academic Press, Inc.