|VAIRA, ANNA MARIA - National Research Council - Italy|
|LIM, HYOUN-SUB - Chungnam National University|
|MIOZZI, L - National Research Council - Italy|
|VINALS, N - National Research Council - Italy|
Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2018
Publication Date: 3/20/2018
Citation: Vaira, A., Lim, H., Bauchan, G.R., Miozzi, L., Vinals, N., Natilla, A., Owens, R.A., Hammond, J. 2018. The interaction of Lolium latent virus major coat protein with ankyrin repeat protein NbANKr redirects it to chloroplasts and modulates virus infection. Plant Journal. 99(5):730-742. https://doi.org/10.1099/jgv.0.001043.
Interpretive Summary: Plant viruses cause significant disease losses in many crops; an understanding of the mechanisms of virus interactions with their hosts necessary for infection and systemic movement may lead to methods for interfering with the infection process, thus reducing losses to disease. Lolium latent virus (LoLV) is unusual among flexuous viruses in having two carboxy-coterminal coat proteins incorporated into virions in approximately equimolar proportion. Previous research has shown that the larger coat protein has an amino-terminal signal sequence suspected to target the coat protein to the chloroplast; here it is shown that the amino-terminal signal sequence does in fact act as a chloroplast transit peptide. It has now also been demonstrated that both forms of the coat protein interact with a host protein containing an ankyrin repeat sequence. Interaction between the LoLV coat protein and the host ankyrin repeat protein was shown to be necessary for efficient systemic movement of the virus, whereas reducing the level of expression of the ankyrin repeat protein was not found to cause any visibly altered phenotype in plants not infected with LoLV. Reduction in expression of the host ankyrin repeat protein may thus offer a potential way of reducing virus infection, and thus reducing disease losses.
Technical Abstract: Lolium latent virus coat proteins (CPs) are here shown to interact with NbANKr host protein during virus infection. This interaction leads to chloroplast targeting of both CPs and eventually to CP internalization, by chloroplast transit peptide (cTP) action. In transient expression, the cTP sequence, other than being responsible for viral CP diverse subcellular localizations, has similar effect on marker genes, further suggesting its key targeting role in vivo during virus infection. To investigate the role of NbANKr in LoLV infection, we analyzed subcellular localization of NbANKr protein and its remarkable interaction with LoLV coat proteins in vivo by BiFC. We successfully used a Tobacco rattle virus vector to silence ANKr genes in Nicotiana benthamiana plants prior to challenge by LoLV mechanical inoculation. When the NbANKr gene was strongly silenced, LoLV infection was greatly reduced in young leaves, compared to levels of replication in control plants, suggesting an impasse in virus movement. Silencing of NbANKr has no obvious effect on plant phenotype but does interfere with LoLV infection, opening the way for new strategies to control virus infection.