Effects of mutations in the beet western yellows virus readthrough protein on its expression and packaging and on virus accumulation, symptoms, and aphid transmission.

摘要

To map different biological functions to the conserved and non-conserved sequence motifs of the readthrough domain (RTD) of beet western yellows luteovirus (BWYV), short in-frame deletions were introduced at different sites in the RTD and mutant genomes were transmitted to protoplasts as transcripts and to Nicotiana clevelandii by agroinfection. Deletions in the non-conserved portion of the RTD did not block aphid transmission, but had a moderately inhibitory effect on virus accumulation in plantsand abolished symptoms. Deletion of the proline tract and the junction between the conserved and nonconserved regions inhibited readthrough protein accumulation in protoplasts by at least 10 times. The mutants accumulated small amounts of virus in plants, did not induce disease symptoms and were nontransmissible by aphid vectors using agroinfected plants, extracts of infected protoplasts or purified virus as sources of inoculum. Other deletions in the conserved portion of the RTD did not significantly decrease readthrough protein accumulation, but abolished its incorporation into virions. The mutants accumulated to low levels in agroinfected plants and elicited symptoms, but were not transmitted by aphids. A preliminary map has been produced mapping the functions to different parts of the RTD.