Effect of C-terminal deletions in the movement protein of cowpea chloroticmottle virus on cell-to-cell and long-distance movement

In order to elucidate the function of the C-terminal region of cowpea chlor otic mottle bromovirus (CCMV) movement protein (MP) in cell-to-cell movemen t, a set of deletions ranging from 10 to 80 amino acids (Delta MP10, Delta MP20, Delta MP33, Delta MP43, Delta MP60 and Delta MP80) was engineered int o the MP gene encoded by the biologically active clone C3/Delta CP-EGFP, a variant of CCMV RNAS that contained wild-type (wt) MP and the enhanced gree n fluorescent protein (EGFP) gene in place of the coat protein (CP), The ef fect of each MP deletion on cell-to-cell movement was examined in three sus ceptible host plants: Chenopodium quinoa, Nicotiana benthamiana and cowpea (Vigna sinensis cv, Black Eye). The results indicate that, except for mutan t Delta MP43, infections resulting from the deletion mutants remained subli minal. Interestingly, infections resulting from inoculating mutant Delta MP 43, which lacked the 43 most C-terminal amino acids, spread rapidly between cells and the number of infected cells expressing EGFP approached that of control inoculations made with C3/Delta CP-EGFP. To verify whether the pres ence of wt CP altered the movement behaviour of these mutants, each MP dele tion was also incorporated into the genetic background of wt CCMV RNA3 (pCC 3) and inoculated independently to all three hosts. The results suggest tha t the overall movement process exhibited by each MP mutant is influenced pr ofoundly by the presence of CP and the particular host plant tested.