Being sessile in nature, plants are subject to a variety of abiotic and biotic stress, under which endoplasmic reticulum (ER)-nucleus communication is activated by two unfolded protein response (UPR) pathways, the S1P/S2P-bZIP17/bZIP28 arm and the IRE1-bZIP60 mRNA branch. Functional transcription factors are liberated to the nucleus to regulate the UPR signature genes via posttranslational modification or unconventional splicing.
The upregulation of UPR signature genes is used as a hallmark of UPR activation. However, upregulation of the UPR genes is far downstream in the UPR pathway and is often promoted by other stress events. Moving yet another step upstream of the UPR gene expression, the modified bZIP17 and bZIP28 as well as the spliced bZIP60 mRNA can serve as surrogates for indicating UPR activation. Nevertheless, questions still existing in this strategy include: how does the bZIP60 mRNA access to its splicing factor IRE1 homologs? Is the splicing carried out independently of or synchronously with translation? How is the spliced bZIP60 mRNA ligated in vivo? What is the working model on the splicing, ligating and translation of the bZIP60 mRNA?
UPR signaling is initiated by the accumulation of misfolded proteins in the ER, however, it is difficult to track the mass of misfolded proteins in the ER. The effects on the ER-resident transducers imposed by misfolded proteins can be an alternative to monitoring whether the UPR is truly initiated. In plants, the bZIP17, bZIP28 and IRE1 homologs act on the front line as transducers sensing ER stress and initiating UPR signaling. However, the interacting model between bZIP17, bZIP28 or IRE1 homologs and misfolded proteins or BiP homolog has not been illustrated experimentally. The question of whether the plant IRE1 homologs cluster, whereby their cytoplasmic domain is activated, is unanswered. Therefore, further studies, especially the genetic and structural elucidation on plant ER transducers, are needed to move us closer to the hub of the UPR activation.
We welcome the submission of Original Research, Systematic Review, Methods, and Perspective, with potential topics including, but are not limited to the following subtopics:
• Advanced approaches to monitor the UPR activation in vivo
• Genetic screening the partner(s) that bind the luminal domains of the ER transducers
• The interaction model between misfolded proteins or chaperons and the ER transducers
• Does the UPR function under normal conditions, and can the UPR be activated without misfolded proteins?
• Genetic evidence for the involvement of potential enzyme(s) in the ligating two half spliced bZIP60 mRNA molecules
• How do bZIP60 mRNA, IRE1 homologs and ribosome coordinate in the unconventional splicing progress
• How do the abiotic stresses elicit the UPR, via misfolded proteins or a feed-back regulation?
• Are bacterial or viral infections activating the UPR via the accumulation of misfolded proteins? What are the key bacterial effectors or viral factors that can induce the UPR?
Being sessile in nature, plants are subject to a variety of abiotic and biotic stress, under which endoplasmic reticulum (ER)-nucleus communication is activated by two unfolded protein response (UPR) pathways, the S1P/S2P-bZIP17/bZIP28 arm and the IRE1-bZIP60 mRNA branch. Functional transcription factors are liberated to the nucleus to regulate the UPR signature genes via posttranslational modification or unconventional splicing.
The upregulation of UPR signature genes is used as a hallmark of UPR activation. However, upregulation of the UPR genes is far downstream in the UPR pathway and is often promoted by other stress events. Moving yet another step upstream of the UPR gene expression, the modified bZIP17 and bZIP28 as well as the spliced bZIP60 mRNA can serve as surrogates for indicating UPR activation. Nevertheless, questions still existing in this strategy include: how does the bZIP60 mRNA access to its splicing factor IRE1 homologs? Is the splicing carried out independently of or synchronously with translation? How is the spliced bZIP60 mRNA ligated in vivo? What is the working model on the splicing, ligating and translation of the bZIP60 mRNA?
UPR signaling is initiated by the accumulation of misfolded proteins in the ER, however, it is difficult to track the mass of misfolded proteins in the ER. The effects on the ER-resident transducers imposed by misfolded proteins can be an alternative to monitoring whether the UPR is truly initiated. In plants, the bZIP17, bZIP28 and IRE1 homologs act on the front line as transducers sensing ER stress and initiating UPR signaling. However, the interacting model between bZIP17, bZIP28 or IRE1 homologs and misfolded proteins or BiP homolog has not been illustrated experimentally. The question of whether the plant IRE1 homologs cluster, whereby their cytoplasmic domain is activated, is unanswered. Therefore, further studies, especially the genetic and structural elucidation on plant ER transducers, are needed to move us closer to the hub of the UPR activation.
We welcome the submission of Original Research, Systematic Review, Methods, and Perspective, with potential topics including, but are not limited to the following subtopics:
• Advanced approaches to monitor the UPR activation in vivo
• Genetic screening the partner(s) that bind the luminal domains of the ER transducers
• The interaction model between misfolded proteins or chaperons and the ER transducers
• Does the UPR function under normal conditions, and can the UPR be activated without misfolded proteins?
• Genetic evidence for the involvement of potential enzyme(s) in the ligating two half spliced bZIP60 mRNA molecules
• How do bZIP60 mRNA, IRE1 homologs and ribosome coordinate in the unconventional splicing progress
• How do the abiotic stresses elicit the UPR, via misfolded proteins or a feed-back regulation?
• Are bacterial or viral infections activating the UPR via the accumulation of misfolded proteins? What are the key bacterial effectors or viral factors that can induce the UPR?
