| Description: | The mechanism by which RNA molecules travel long distances through plant vasculature is unknown. We study systemic transport of two types of RNA: plant virus genomes and elicitors of post translational gene silencing (PTGS). We demonstrated that exposure of plants to non-toxic concentrations of cadmium (Cd) block viral disease. Cd-mediated viral protection was due to inhibition of the systemic movement of the virus but had no effect on viral replication and local spread. Furthermore, higher, toxic levels of Cd did not inhibit viral systemic movement (Plant J. 13, 591-602). Thus, non-toxic levels of Cd may trigger production of cellular factors which interfere with the viral systemic movement; exposure of plants to higher, toxic amounts of Cd likely represses this defensive response.Confocal immunofluorescence showed that, in the infected plants exposed to non-toxic levels of Cd, virions entered the vascular tissue but were unable to exit it into the non-inoculated, systemic organs. Thus, viral entry into and exit from the vascular cells may occur by different mechanisms. Furthermore, low Cd concentrations did not induce acquired resistance and acted independently of salicylic acid and pathogenesis related (PR) proteins (Plant J. 16, 13-20). Because viruses often adapt existing cellular machinery for their needs, they likely employ an endogenous pathway for systemic transport of RNA. Recent evidence indicates that cellular RNAs also travel through plant vasculature, revealing a novel type of systemic signaling. Specifically, PTGS, an innate plant defense mechanism, is likely elicited by such RNA signals. Our recent experiments indicate the low levels of Cd reverse PTGS, resulting in 'unsilencing' of the repressed marker genes and suggesting that viral systemic movement and PTGS may share similar transport pathways within plants. Microarray technology is especially useful to identify transcripts selectively induced or repressed under different experimental conditions. As our data indicate that Arabidopsis plants (Col-0 and Col-1) respond to low Cd concentrations by restricting viral systemic movement, we propose to perform Arabidopsis cDNA microarray experiments to identify genes induced or repressed in plants treated with non-toxic (viral movement and PTGS are restricted) but not toxic concentrations of Cd (viral movement and PTGS are not restricted). The results of these experiments may shed new light on plant factors involved in systemic traffic of RNA. |
NASCArrays Information at The BAR
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