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Abstract The endoplasmic reticulum (ER) immunoglobulin binding proteins (BiPs) are molecular chaperones involved in normal protein maturation and refolding malformed proteins through the unfolded protein response (UPR). Plant BiPs belong to a multi-gene family contributing to development, immunity, and responses to environmental stresses. This study identified threeBiPhomologs in theSolanum tuberosum(potato) genome using phylogenetic, amino acid sequence, 3-D protein modeling, and gene structure analysis. These analyses revealed thatStBiP1andStBiP2grouped withAtBiP2, whereasStBiP3grouped withAtBiP3. While the protein sequences and folding structures are highly similar, theseStBiPsare distinguishable by their expression patterns in different tissues and in response to environmental stressors such as treatment with heat, chemicals, or virus elicitors of UPR. Ab initio promoter analysis revealed that potato and ArabidopsisBiP1andBiP2promoters were highly enriched with cis-regulatory elements (CREs) linked to developmental processes, whereasBiP3promoters were enriched with stress related CREs. The frequency and linear distribution of these CREs produced two phylogenetic branches that further resolve the groups identified through gene phylogeny and exon/intron phase analysis. These data reveal that the CRE architecture ofBiPpromoters potentially define their spatio-temporal expression patterns under developmental and stress related cues. 

Summary IRE1, BI‐1, and bZIP60 monitor compatible plant–potexvirus interactions though recognition of the viral TGB3 protein. This study was undertaken to elucidate the roles of threeIRE1isoforms, thebZIP60UandbZIP60S, andBI‐1roles in genetic reprogramming of cells during potexvirus infection.Experiments were performed usingArabidopsis thalianaknockout lines andPlantago asiatica mosaic virusinfectious clone tagged with the green fluorescent protein gene (PlAMV‐GFP).There were more PlAMV‐GFP infection foci inire1a/b,ire1c,bzip60, andbi‐1knockout than wild‐type (WT) plants. Cell‐to‐cell movement and systemic RNA levels were greaterbzip60andbi‐1than in WT plants. Overall, these data indicate an increased susceptibility to virus infection. Transgenic overexpression ofAtIRE1borStbZIP60inire1a/borbzip60mutant background reduced virus infection foci, whileStbZIP60expression influences virus movement. Transgenic overexpression ofStbZIP60also confers endoplasmic reticulum (ER) stress resistance following tunicamycin treatment. We also show bZIP60U and TGB3 interact at the ER.This is the first demonstration of a potatobZIPtranscription factor complementing genetic defects in Arabidopsis. Evidence indicates that the three IRE1 isoforms regulate the initial stages of virus replication and gene expression, while bZIP60 and BI‐1 contribute separately to virus cell‐to‐cell and systemic movement.