Maintenance of a stem loop structure is essential for the translation of the Potato leafroll virus minor capsid protein that regulates local virus movement in phloem tissues    
Y. XU (1), S. Gray (2) (1) Cornell University, U.S.A.; (2) Cornell University; USDA-ARS, Robert W. Holley Center for Agriculture and Health, U.S.A.

Translational read-through of the capsid protein UAG stop codon is an evolutionarily conserved feature that members of the Luteoviridae have adopted to produce the minor capsid protein (RTP). The elements regulating RTP expression are not well understood, but involve long distance interactions between RNA domains. We identified a cistine-rich domain and a complex stem loop structure located immediately downstream and 640 nucleotides downstream of the CP stop codon, respectively. Deletion and site directed mutants indicate that the distance and sequence composition between the two domains is flexible, as is the sequence and structure of some aspects of the 90 nucleotide distal domain. However, base pairing in one stem-loop region is critical for efficient RTP translation and normal systemic infection of host plants. Unexpectedly, plants infected with the stem-loop mutants developed a wild type virus infection phenotype 7-8 weeks post-inoculation due to compensatory mutations that restored the critical stem loop structure. RTP translation is not critical for long distance movement of virus as these mutants can spread from inoculated tissues, but fewer infection foci develop in systemically infected leaves. RTP is localized to plasmodesmata of virus-infected cells, but if the cell-to-cell movement protein is present. By mutagenic analysis, we found RTP-MP17 binding is crucial for PLRV move efficiently within newly infected tissues. There is a strong selection pressure to maintain secondary RNA structures that regulate RTP translation and subsequent efficient local spread of virus.

Abstract Number: C8-3
Session Type: Concurrent