STUDIES OF COAT PROTEIN-MEDIATED RESISTANCE TO TOBACCO MOSAIC-VIRUS (TMV) .2. CHALLENGE BY A MUTANT WITH ALTERED VIRION SURFACE DOES NOT OVERCOME RESISTANCE CONFERRED BY TMV COAT PROTEIN

Transgenic tobacco plants expressing the coat protein (CP) gene of the U1 strain of tobacco mosaic virus (TMV) exhibit CP-mediated resistanc e (CP-MR) against some, but not all, tobamoviruses. To investigate the role of the amino acid sequences on the surface of the challenge viru s in CP-MR, mutant strains of U1 TMV were constructed to contain the a mino or carboxy termini of the CP of Sunn hemp mosaic tobamovirus (SHM V). The modified virus was unable to overcome CP-MR in transgenic plan ts that contained the TMV CP. In contrast, TMV in which the CP was rep laced by the SHMV CP overcame CP-MR to the same extent as did SHMV. We conclude that CP-MR conferred by TMV CP involves interactions between amino acid sequences of the challenge viruses and the transgene prote in other than those on the surface of the challenge virus.