Virus recovery is induced in Brome mosaic virus p2 transgenic plants showing synchronous complementation and RNA-2-specific silencing.
Nicotiana benthamiana plants expressing Brome mosaic virus (BMV) p2 protein complemented replication of RNAs1 + 3 but, surprisingly, supported little or no replication of RNA-2. Despite this, the p2 transgenic plants were able to support systemic migration of RNAs-1 and -3. Kinetic analyses showed identical degradation rates for RNAs-2 and -3, greatly detracting from the concept of an induction of an RNA-2-specific degradation system. Deletion analysis identified a 200-nucleotide sequence that may contribute to silencing in a context-specific manner. When R1 progeny of a severely silencing p2 transgenic line were tested for virus resistance, three different classes of reactions were observed. In class 1 and class 3 plants, the virus moved systemically and showed various extents of RNA-2 silencing. However, in class 2 plants, there was a stochastic onset of post-transcriptional silencing in the systemic leaves that was reminiscent of virus recovery. Plants showing recovery tended to have a greater number of transgene loci than did those exhibiting component-specific silencing. The induction of silencing did not appear to be dependent solely on the combined steady state levels of the transgene and viral RNA. Some plants transformed with a p2 frameshift construct showed a complete silencing phenotype, but none showed RNA-2-specific silencing. While the relationship between the two types of silencing remains unclear, we speculate that our observations reflect early events in the induction of virus recovery.
Iyer
L M
LM
Institute of Developmental and Molecular Biology, Texas A&M University, College Station 77843-3155, USA.
Hall
T C
TC
D017795:Bromovirus / Q000235:genetics / Q000502:physiology*; D016368:Frameshift Mutation; D020868:Gene Silencing; D015336:Molecular Probe Techniques; D030821:Plants, Genetically Modified; D010947:Plants, Toxic; D016133:Polymerase Chain Reaction; D012323:RNA Processing, Post-Transcriptional; D012367:RNA, Viral / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000821:virology*; D014162:Transfection; D014764:Viral Proteins / Q000235:genetics*; D014779:Virus Replication
D012367:RNA, Viral; D014764:Viral Proteins