Characterization and expression of the Douglas-fir luminal binding protein (PmBiP)

The endoplasmic reticulum (ER) molecular chaperone, BiP, plays a role in the cotranslational translocation and subsequent folding and assembly of newly synthesized proteins targeted to the ER and secretory pathway. The sequence encoding a Douglas-fir (Pseudotsuga menziesii [Mirb] Franco) BiP homologue (PmBiP) was identified by differential screening of a seedling cDNA library. Southern blotting indicated that PmBiP is most likely present as a single copy. The deduced amino acid sequence of PmBiP contains an HEEL tetrapeptide sequence which functions to retain PmBiP in the ER and is different from HDEL commonly found in angiosperm plant BiPs. Amino acid sequence alignment and phylogenetic analysis show that PmBiP is highly similar to other plant BiPs yet forms a distinct phylogenetic subgroup which is separate from the angiosperm BiPs. Northern and western blotting revealed that PmBiP is subject to developmental regulation during seed development, germination, and early seedling growth and is seasonally regulated in needles of young seedlings.