Gaining Replicability in a Nonhost Compromises the Silencing Suppression Activity of Tobacco Mild Green Mosaic Virus in a Host

Natural isolates of Tobacco mild green mosaic virus (TMGMV) fail to infect tomato because the tomato tm-1 protein binds to the replication proteins of TMGMV and prevents RNA replication. Previously, we isolated a TMGMV mutant that overcomes tm-1-mediated resistance and multiplies in tomato plants. Here, we show that the causal mutations in the replication protein gene that abolish the interaction with tm-1 reduce its ability to suppress RNA silencing in host plant Nicotiana benthamiana . The results suggest that the multifunctionality of the replication proteins is an evolutionary constraint of tobamoviruses that restricts their host ranges.