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Plant Cell Physiol. 2017 Jun 1;58(6):1103-1117. doi: 10.1093/pcp/pcx057.

A Non-Classical Member of the Protein Disulfide Isomerase Family, PDI7 of Arabidopsis thaliana, Localizes to the cis-Golgi and Endoplasmic Reticulum Membranes.

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University of Hawaii, Molecular Biosciences & Bioengineering, Honolulu, HI, USA.
Chinese University of Hong Kong, Centre for Cell and Developmental Biology, State Key Laboratory of Agrobiotechnology, Shatin, Hong Kong, China.


Members of the protein disulfide isomerase (PDI)-C subfamily are chimeric proteins containing the thioredoxin (Trx) domain of PDIs, and the conserved N- and C-terminal Pfam domains of Erv41p/Erv46p-type cargo receptors. They are unique to plants and chromalveolates. The Arabidopsis genome encodes three PDI-C isoforms: PDI7, PDI12 and PDI13. Here we demonstrate that PDI7 is a 65 kDa integral membrane glycoprotein expressed throughout many Arabidopsis tissues. Using a PDI7-specific antibody, we show through immunoelectron microscopy that PDI7 localizes to the endoplasmic reticulum (ER) and Golgi membranes in wild-type root tip cells, and was also detected in vesicles. Tomographic modeling of the Golgi revealed that PDI7 was confined to the cis-Golgi, and accumulated primarily at the cis-most cisterna. Shoot apical meristem cells from transgenic plants overexpressing PDI7 exhibited a dramatic increase in anti-PDI7 labeling at the cis-Golgi. When N- or C-terminal fusions between PDI7 and the green fluorescent protein variant, GFP(S65T), were expressed in mesophyll protoplasts, the fusions co-localized with the ER marker, ER-mCherry. However, when GFP(S65T) was positioned internally within PDI7 (PDI7-GFPint), the fusion strongly co-localized with the cis-Golgi marker, mCherry-SYP31, and faintly labeled the ER. In contrast to the Golgi-resident fusion protein (Man49-mCherry), PDI7-GFPint did not redistribute to the ER after brefeldin A treatment. Protease protection experiments indicated that the Trx domain of PDI7 is located within the ER/Golgi lumen. We propose a model where PDI-C isoforms function as cargo receptors for proteins containing exposed cysteine residues, cycling them from the Golgi back to the ER.


Secretory pathway; cargo receptor; cis-Golgi; endoplasmic reticulum; membrane protein traffic; protein disulfide isomerase

[Indexed for MEDLINE]

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