STIP1 and infection: In summary, the knockdown of Hop/Sti1 by RNAi does not affect the induction of the UPR or the affiliated programmed cell death reaction in response to PVYN or tunicamycin in Nicotiana tabacum leaves, i.e., the Hop/Sti1-dependent formation of PVYN infection symptoms does not stem from the induction of ER stress-mediated cell death.