Expression of many host genes are altered during virus infection, and this change can in turn affect the defense response. We have obtained the CDS of a gene, designated NbTrm, which encodes an m-type thiroredoxin in tobacco, using a homology-based cloning method. The CDS of NbTrm is 549 bp in length, and encodes a predicted protein with a thiroredoxin super family conserved domain in the C terminus. Potato virus Y (PVY) is the type member of the family Potyviridae. In a study of PVY infection in Nicotina benthamiana, we observed that the expression of NbTrm was up-regulated at about 10 days post-inoculation (dpi) by semi-quantitative PCR. We also determined that virus-induced gene silencing (VIGS) of NbTrm in tobacco by using the pgR106 vector system significantly enhanced PVY accumulation as determined by Northern blotting. In contrast, transient over-expression of NbTrm in tobacco protoplasts by PEG-mediated transfection showed that increasing NbTrm expression could inhibit the amplification of PVY viral RNA. Our preliminary data suggests that Nbtrm, which encodes an m-type thiroredoxin, can be up-regulated by potyvirus infection and plays an inhibitory role during PVY infection of tobacco cells.