Alfalfa mosaic virus infection downregulates a vital photosynthesis gene.

摘要

Alfalfa mosaic virus (AMV) is a single stranded RNA virus whose genome codes for four proteins. One of these viral proteins, coat protein, encapsidates AMV RNA. The requirement of coat protein (CP) or its messenger RNA for infectivity makes AMV unique among other viruses in the Bromoviridae family. Host proteins take part in different stages of the life cycle of viruses. A number of Arabidopsis proteins were found to interact with AMV CP in yeast two hybrid screens. One of the positive yeast colonies contained a full length cDNA encoding the photosynthetic protein, PsbP. We chose to further investigate PsbP based upon several reports that indicate that photosynthetic proteins are downregulated upon virus infection. In this study our objectives were to, (1) determine the interaction of CP and PsbP in vivo by Bimolecular Fluorescence Complementation (BiFC), (2) determine if silencing of psbP transcripts changes the susceptibility of Nicotiana tabacum to AMV, and (3) determine if psbP transcripts are downregulated upon AMV infection in WT N. tabacum. Fluorescence was detected in Arabidopsis protoplasts transfected with a vector encoding the full length enhanced yellow fluorescent protein (EYFP), but not in protoplasts transfected with vectors encoding CP:EYFP fragment fusions. We discovered that silencing of the psbP transcripts in N.tabacum plants increased the susceptibility of the plants to AMV. In the group I silenced plants, there was a 4 fold increase in the accumulation of AMV after 5 days post infection (dpi), and a 40 fold increase in accumulation AMV accumulation in the group II silenced plants. We also discovered that the psbP transcripts were downregulated upon AMV infection in WT N.tabacum plants. After 5dpi, group I psbP transcripts were downregulated by 81%-83% and group II psbP transcripts were downregulated by 45%.