PARP1 and infection: First, our results showed that the substantial increase in endogenous concentrations of both free SA and conjugated SA (SA-b-glucoside) [52,53] during TRV infection in inoculated and both old and newly emerging systemically infected leaves (compared to mock-inoculated plants) [29] coincided with nucleolar retention of PARP1, over-accumulation of PARylated proteins and TRV recovery (Figure 1b and Figure 3).