LAUSR

The unfolded protein response (UPR), a highly conserved cellular defense pathway, is activated by endoplasmic reticulum (ER) stress. In Arabidopsis, the transcription factor AtbZIP28 mediates ER stress responses induced by tunicamycin. Here, we identified NbbZIP28 in Nicotiana benthamiana. Sequence analyses showed that the NbbZIP28 encodes a protein of 812 amino acids with a putative transmembrane domain (TMD) near its C terminus next to a basic leucine zipper domain. In localization analyses, NbbZIP28 was located in the ER, and NbbZIP28∆C, a truncated form of NbbZIP28 that lacked the region from the TMD to the carboxy terminus, localized in the nucleus. The transcript levels of NbbZIP28 were significantly up-regulated at 48 h post inoculation with Cucumber mosaic virus and Tobacco mosaic virus. NbbZIP28-silenced N. benthamiana plants showed no significant phenotypic change, but viruses were able to accumulate to higher levels in the silenced plants than in control plants. The NbbZIP28-silenced plants showed lower transcript levels of UPR genes including BiP and NF-YC2 at the early stage of virus infection, although the transcript levels recovered or even increased at a later stage, indicating that NbbZIP28 may be a key regulator, among others, of UPR,. In summary, the ER-localized transcription factor NbbZIP28 may play a role in the defense response against viruses by promoting the UPR pathway activation in N. benthamiana.