Replication of TMV-L and Lta1 RNAs and their recombinants in TMV-resistant Tm-1 tomato protoplasts.

Tm-1 is a gene that provides resistance to tomato plants against tobacco mosaic virus (TMV) infection. In tomato cells carrying the Tm-1 gene, multiplication of TMV is inhibited. From previous analysis of resistance-breaking mutants, the involvement of the 130- and 180-kDa proteins, putative viral replicases, in the resistance conferred by the Tm-1 gene was suggested. When wild-type TMV RNA was co-inoculated with a resistance-breaking mutant RNA, replication of the wild-type TMV genomic RNA could not be rescued by the 130- and 180-kDa proteins of a resistance-breaking strain, Lta1. To investigate how the putative resistance factor interacts with the 130- and 180-kDa proteins, we expressed the wild-type TMV protein sequence that is associated with the resistance-breaking phenomenon as part of a recombinant virus derived from Lta1 in Tm-1/Tm-1 protoplasts. No specific degradation of wild-type TMV protein sequences was observed, suggesting that the mechanism of the resistance does not involve the instability of a viral protein.