Cucumber mosaic virus-plant interactions: Identification of 3a protein sequences affecting infectivity, cell-to-cell movement, and long-distance movement

Mutants of the Cucumber mosaic virus (CMV) movement protein(MP) were genera ted and analyzed for their effects on virus movement and pathogenicity in v ivo. Similar to the wild-type MP, mutants M1, M2, and M3, promoted virus mo vement in eight plant species, Mutant M3 showed some differences in pathoge nicity in one host species. Mutant M8 showed some host-specific alterations in movement in two hypersensitive hosts of CMV, Mutant M9 showed altered p athogenicity on three hosts and was temperature sensitive for long-distance movement, demonstrating that cell-to-cell and long-distance movement are d istinct movement functions for CMV, Four mutants (M4, M5, M6, and M7) were debilitated from movement in all hosts tested. Mutants M4, M5, and M6 could be complemented in trans by the wild-type MP expressed transgenically, alt hough not by each other or by mutant M9 (at the restrictive temperature). M utant M7 showed an inability to be complemented in trans. From these mutant s, different aspects of the CMV movement process could be defined and speci fic roles for particular sequence domains assigned. The broader implication s of these functions are discussed.