MOLECULAR-BASIS FOR VIRUS-DISEASE RESISTANCE IN PLANTS

Classical studies of virus disease resistance in plants have provided the basis for recent molecular studies of resistance. Three common app roaches to the study of resistance have been used. In one approach, nu cleotide and/or amino acid sequences of virus strains that overcome di sease resistance genes in the host are compared with sequences of stra ins that do not induce disease in these hosts. In the second approach, resistance/susceptibility of protoplasts is compared with the respons e of intact plants from which they are derived, to develop hypotheses regarding whether resistance acts at the level of the individual cell or by inhibiting cell-to-cell movement. In the third approach, the mec hanism of virus cell-to-cell movement has been studied to clarify one of the basic steps in pathogenesis and to determine the mechanism of d isease resistance for certain virus-host interactions.