Abstract
BackgroundDespite the relevance of the eukaryotic endoplasmic reticulum (ER)-stress response as an integrator of multiple stress signals into an adaptive response, knowledge about these ER-mediated cytoprotective pathways in soybean (Glycine max) is lacking. Here, we searched for genes involved in the highly conserved unfolded protein response (UPR) and ER stress-induced plant-specific cell death signaling pathways in the soybean genome.MethodsPreviously characterized Arabidopsis UPR genes were used as prototypes for the identification of the soybean orthologs and the in silico assembly of the UPR in soybean, using eggNOG v4.0 software. Functional studies were also conducted by analyzing the transcriptional activity of soybean UPR transducers.ResultsAs a result of this search, we have provided a complete profile of soybean UPR genes with significant predicted protein similarities to A. thaliana UPR-associated proteins. Both arms of the plant UPR were further examined functionally, and evidence is presented that the soybean counterparts are true orthologs of previously characterized UPR transducers in Arabidopsis. The bZIP17/bZI28 orthologs (GmbZIP37 and GmbZIP38) and ZIP60 ortholog (GmbZIP68) from soybean have similar structural organizations as their Arabidopsis counterparts, were induced by ER stress and activated an ERSE- and UPRE-containing BiP promoter. Furthermore, the transcript of the putative substrate of GmIREs, GmbZIP68, harbors a canonical site for IRE1 endonuclease activity and was efficiently spliced under ER stress conditions. In a reverse approach, we also examined the Arabidopsis genome for components of a previously characterized ER stress-induced cell death signaling response in soybean. With the exception of GmERD15, which apparently does not possess an Arabidopsis ortholog, the Arabidopsis genome harbors conserved GmNRP, GmNAC81, GmNAC30 and GmVPE sequences that share significant structural and sequence similarities with their soybean counterparts. These results suggest that the NRP/GmNAC81 + GmNAC30/VPE regulatory circuit may transduce cell death signals in plant species other than soybean.ConclusionsOur in silico analyses, along with current and previous functional data, permitted generation of a comprehensive overview of the ER stress response in soybean as a framework for functional prediction of ER stress signaling components and their possible connections with multiple stress responses.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1952-z) contains supplementary material, which is available to authorized users.
Highlights
Despite the relevance of the eukaryotic endoplasmic reticulum (ER)-stress response as an integrator of multiple stress signals into an adaptive response, knowledge about these ER-mediated cytoprotective pathways in soybean (Glycine max) is lacking
Because the plant unfolded protein response (UPR) is transduced as a bipartite module that converges in an adaptive response, we have presented our data in the following groups to facilitate comprehension: UPR transducers/ sensors, UPR immediate downstream components and UPR downstream components (Table 1)
Despite the relevance of the ER as a key organelle involved in stress adaptive responses, genes involved in the ER stress response in soybean have not been examined to date
Summary
Despite the relevance of the eukaryotic endoplasmic reticulum (ER)-stress response as an integrator of multiple stress signals into an adaptive response, knowledge about these ER-mediated cytoprotective pathways in soybean (Glycine max) is lacking. We searched for genes involved in the highly conserved unfolded protein response (UPR) and ER stress-induced plant-specific cell death signaling pathways in the soybean genome. The UPR operates as a tripartite module, and the ER stress signal is transduced through the ER membrane receptors protein kinase-like ER kinase (PERK), inositol-requiring transmembrane kinase and endonuclease 1α (IRE1) and activation of transcription factor 6 (ATF6) [2]. Upon disruption of ER homeostasis, plant cells activate at least two branches of the UPR through IRE1-like and ATF6-like transducers, resulting in the up-regulation of ER-resident molecular chaperones and activation of the ER-associated protein degradation system. A plasma membraneassociated member of the plant-specific NAC domaincontaining TF family, AtNAC62, has been demonstrated to undergo cross-talk with ER stress signaling pathways to activate UPR-induced promoters, highlighting a unique aspect of this highly conserved UPR response in plants [6]
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