Identification and study of tobacco mosaic virus movement function by complementation tests

The phenomenon of trans-complementation of cell-to-cell movement between pl ant positive-strand RNA viruses is discussed with an emphasis on tobamoviru ses. Attention is focused on complementation between tobamoviruses (coding for a single movement protein, RIP) and two groups of viruses that contain the triple block of MP genes and require four (potato virus X) or three (ba rley stripe mosaic virus) proteins for cell-to-cell movement. The highlight s of complementation data obtained by different experimental approaches are given, including (i) double infections with movement-deficient (dependent) and helper viruses; (ii) infections with recombinant viral genomes bearing a heterologous MP gene; (iii) complementation of a movement-deficient viru s in transgenic plants expressing the MP of a helper virus; and (iv) co-bom bardment of plant tissues with the cDNAs of a movement-dependent virus geno me and the MP gene of a helper virus.