Poster: Organelle biogenesis

Abs # 641: Immunolocalization of a protein disulfide isomerase to chloroplasts of Arabidopsis and its association with starch granule biogenesis.

Presenter:	Christopher, David A, dchr@hawaii.edu
Authors	Christopher, David A (A)   Lu, Dong-Ping  (A) (A)
Affiliations:	(A): University of Hawaii

The protein disulfide isomerase (PDI) gene family in Arabidopsis consists of 11 members that differ in polypeptide length from 361 to 566 amino acids, presence of signal peptides, KDEL motifs, and the number and positions of thioredoxin domains. In the endoplasmic reticulum (ER), PDI's catalyze the reversible formation and isomerization of disulfide bonds necessary for the proper folding, assembly, activity, and secretion of numerous enzymes and structural proteins. PDI's have also evolved novel cellular redox functions, as single enzymes and as subunits of protein complexes in organelles. In vitro translation of all 11 different PDI’s followed by microsomal membrane processing reactions were used to differentiate among PDI’s localized in the ER or to other organelles. To further pinpoint PDI functions, we have used PDI-specific antisera on western blots and via immunofluorescence light microscopy to show that a PDI (55 kDa) is present in chloroplasts. PDI-55 levels are very low in the dark and increase with light intensity. PDI-55 assembles into a high molecular weight complex of ~230 kDa as determined on native blue gels. Using transmission electron microscopy, we observed that PDI antisera specifically localizes in an asymmetric orientation to the early stages of developing starch granules. We propose a new role for a PDI in plants, that of modulating starch granule biogenesis (Supported by NSF grant MCB03-48028).