Viral infection-induced endoplasmic reticulum stress and a membrane-associated transcription factor NbNAC089 are involved in resistance to virus in Nicotiana benthamiana

Abstract

Endoplasmic reticulum (ER) stress may induce two cell defence pathways, the unfolded protein response (UPR) or programmed cell death (PCD) upon unmitigated stress. This study confirmed that viral infection could induce ER stress through changing ER morphology and up-regulating ER stress-related genes, including NbNAC089. AtNAC089 serves as an ER stress sensor to regulate PCD in Arabidopsis. In this study, Nicotiana benthamiana NbNAC089 was identified. The gene encoded a 409 amino acid protein with a putative transmembrane domain near the C-terminus and a NAC domain at the N-terminus. NbNAC089 was localized to the ER membranes, and a truncated form of NbNAC089, lacking the transmembrane domain, was localized to the nucleus. Meanwhile, the full length of NbNAC089 was activated and cleaved in response to viral infection. The results suggest that the native protein may be translocated to the nucleus by release from the membrane during viral infection. Knock-down of NbNAC089 in N. benthamiana increased susceptibility to Tobacco mosaic virus or Cucumber mosaic virus, and, in addition, promoted up-regulation of UPR genes but impaired up-regulation of PCD genes. These results show that NbNAC089 is a negative regulator of UPR and a positive regulator of PCD, and plays a role in the process of viral infection.