Interactions between tobacco bushy top virus and its satellite RNA
Tobacco bushy top disease (TBTD) has caused significant yield and economic losses in Yunnan Province, China. The disease is caused by an unique virus complex consisting of tobacco bushy top virus (TBTV), TBTV satellite RNA, tobacco vein distorting virus, tobacco vein distorting virus-associated RNA, and an unidentified viral RNA. The objectives of this study were to determine the complete genome sequence of TBTV satellite RNA, and to investigate the interactions between TBTV and its satellite RNA, which are the two important components in the TBTD complex. The complete genome sequences of seven TBTV satellite RNA isolates were determined and their molecular variations were evaluated. Agrobacterium-mediated infectious clones of TBTV and its satellite RNA were constructed to facilitate the research. The results showed that TBTV satellite RNA was a new satellite RNA and the identities shared among these seven TBTV satellite RNA isolates ranged from 72.0 % to 99.4 %, with the lowest identities between Yongren isolate and the others. TBTV alone was able to replicate and move systematically and cause mild symptoms in plants (Nicotiana tabacum and N. benthamiana). While the satellite RNA was dependent on TBTV for its replication and systematic movement, it boosted the symptom severity of the disease when co-infected with TBTV. TBTV satellite RNA stimulated mildly the accumulation of TBTV genomic RNA in N. benthamiana, while in N. tabacum, it downregulated the accumulation of TBTV genomic RNA slightly, indicating host specificity in the association of TBTV and its satellite RNA. This study would broaden the understanding of TBTD complex and the mechanism of plant virus interactions, and lead to develop new stratigies in the control of TBTD.