Mechanisms of tomato mosaic virus RNA replication and its inhibition by the host resistance factor Tm-1

• Tm-1 is a semidominant ToMV resistance gene that does not induce a defense reaction.
• Tm-1 was identified as an inhibitor of ToMV replication using a cell-free system.
• Tm-1 binds ToMV replication proteins and inhibits replication complex assembly.

In the plant immune system, sensor proteins encoded by dominant resistance genes activate a defense response upon pathogen infection. The tomato mosaic virus (ToMV) resistance gene Tm-1 is exceptional in that it inhibits ToMV multiplication without inducing a defense response. Several lines of evidence had suggested that Tm-1 encodes a direct inhibitor of ToMV RNA replication. The Tm-1 gene product was identified by purification of an inhibitor protein using a cell-free translation and replication system for ToMV RNA. Further analyses using the system showed that Tm-1 bound ToMV replication proteins, and that the Tm-1-bound ToMV replication proteins retained the ability to bind membranes, while Tm-1 inhibited replication complex formation on the membranes.