Unique COPII component AtSar1a/AtSec23a pair is required for the distinct function of protein ER export in Arabidopsis thaliana

Yonglun Zeng, Kin Pan Chung, Baiying Li, Ching Man Lai, Sheung Kwan Lam, Xiangfeng Wang, Yong Cui, Caiji Gao, Ming Luo, Kam-Bo Wong, Randy Schekman, Liwen Jiang*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

62 Citations (Scopus)


Secretory proteins traffic from endoplasmic reticulum (ER) to Golgi via the coat protein complex II (COPII) vesicle, which consists of five cytosolic components (Sar1, Sec23-24, and Sec13-31). In eukaryotes, COPII transport has diversified due to gene duplication, creating multiple COPII paralogs. Evidence has accumulated, revealing the functional heterogeneity of COPII paralogs in protein ER export. Sar1B, the small GTPase of COPII machinery, seems to be specialized for large cargo secretion in mammals. Arabidopsis contains five Sar1 and seven Sec23 homologs, and AtSar1a was previously shown to exhibit different effects on ?-amylase secretion. However, mechanisms underlying the functional diversity of Sar1 paralogs remain unclear in higher organisms. Here, we show that the Arabidopsis Sar1 homolog AtSar1a exhibits distinct localization in plant cells. Transgenic Arabidopsis plants expressing dominant-negative AtSar1a exhibit distinct effects on ER cargo export. Mutagenesis analysis identified a single amino acid, Cys84, as being responsible for the functional diversity of AtSar1a. Structure homology modeling and interaction studies revealed that Cys84 is crucial for the specific interaction of AtSar1a with AtSec23a, a distinct Arabidopsis Sec23 homolog. Structure modeling and coimmunoprecipitation further identified a corresponding amino acid, Cys484, on AtSec23a as being essential for the specific pair formation. At the cellular level, the Cys484 mutation affects the distinct function of AtSec23a on vacuolar cargo trafficking. Additionally, dominant-negative AtSar1a affects the ER export of the transcription factor bZIP28 under ER stress. We have demonstrated a unique plant pair of COPII machinery function in ER export and the mechanism underlying the functional diversity of COPII paralogs in eukaryotes.

Original languageEnglish
Pages (from-to)14360-14365
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number46
Early online date2 Nov 2015
Publication statusPublished - 17 Nov 2015

Scopus Subject Areas

  • General

User-Defined Keywords

  • Coat protein complex II
  • ER export
  • Functional diversity
  • Sar1
  • Sec23


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