The poly(A)-binding protein (PABP) is an important translation initiation factor 
that binds to the polyadenylated 3' end of mRNA. We have previously shown that 
PABP2 interacts with the RNA-dependent RNA polymerase (RdRp) and VPg-Pro of 
turnip mosaic virus (TuMV) within virus-induced vesicles. At least eight PABP 
isoforms are produced in Arabidopsis thaliana, three of which (PABP2, PABP4 and 
PABP8) are highly and broadly expressed and probably constitute the bulk of PABP 
required for cellular functions. Upon TuMV infection, an increase in protein and 
mRNA expression from PAB2, PAB4 and PAB8 genes was recorded. In vitro binding 
assays revealed that RdRp and the viral genome-linked protein (VPg-Pro) interact 
preferentially with PABP2 but are also capable of interaction with one or both 
of the other class II PABPs (i.e. PABP4 and PABP8). To assess whether PABP is 
required for potyvirus replication, A. thaliana single and double pab knockouts 
were isolated and inoculated with TuMV. All lines showed susceptibility to TuMV. 
However, when precise monitoring of viral RNA accumulation was performed, it was 
found to be reduced by 2.2- and 3.5-fold in pab2 pab4 and pab2 pab8 mutants, 
respectively, when compared with wild-type plants. PABP levels were most 
significantly reduced in the membrane-associated fraction in both of these 
mutants. TuMV mRNA levels thus correlated with cellular PABP concentrations in 
these A. thaliana knockout lines. These data provide further support for a role 
of PABP in potyvirus replication.