Differential localization and accumulation of the plant double stranded RNA-dependent protein kinase during virus infection

Phosphorylation of the plant encoded, double-stranded (dsRNA)-dependent protein kinase (pPKR) is significantly enhanced over basal levels during early phases of virus and viroid infection. It is unclear, however, if corresponding pPKR protein levels are affected by pathogenesis. We now show that virus infection differentially effects pPKR protein levels. Significantly, cytosolic associated pPKR protein levels are induced 3–5 fold compared to levels in extracts from mock inoculated leaves. However, ribosome-associated pPKR protein levels from virus infected tissues decreased approximately 4-fold relative to levels in extracts from mock inoculated tissues. Further, the level of cytosolic-associated pPKR capable of binding to dsRNA declined during early TMV infection events suggesting that viral dsRNAʹs bind to pPKR in the cytosol during initial phases of pathogenesis.