The present invention provides trans-complementation systems for
expressing gene products in plants. In general, the invention provides
systems including a carrier vector and a producer vector, both based on
plant viruses. The producer vector is defective for at least one function
needed for successful systemic infection of a plant, e.g., replication,
cell-to-cell movement, or long distance movement. The carrier vector
supplies the missing function in trans. Certain producer vectors lack a
functional coat protein coding sequence, in which case the corresponding
producer vector supplies coat protein in trans. The invention also
provides novel plant viral vectors and methods of use, e.g., to produce
polypeptides or active RNAs in plants.