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

Abstract

Secretory proteins traffic from endoplasmic reticulum (ER) to Golgi via the coat protein complex II (COPII) vesicle, which consists of five cytosolic components (Sar1,. 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 α-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.coat protein complex II | Sar1 | Sec23 | ER export | functional diversity

Adaptor Protein-3-Dependent Vacuolar Trafficking Involves a Subpopulation of COPII and HOPS Tethering Proteins

“…It was proposed recently that different Sar-1 paralogs encoded in plant genomes may have distinct functions (Chung et al, 2016). Indeed, an amino acid difference determines the separate function of two Sar-1s (Zeng et al, 2015). The tonoplast association of CBL6 was unaffected by interfering with the formation of Sar-1b-positive COPII (Batistic et al, 2010), which is also true for PAT10 (Fig.…”

“…A recent study indicated that, although different Sar-1s in Arabidopsis share high sequence homology, their function might be distinct (Zeng et al, 2015). Realtime quantitative PCR showed that Sar-1b and Sar-1c are constitutively expressed, while the transcript level of Sar-1a is low in all tissues examined (Supplemental Fig.…”

Secretory COPII Protein SEC31B Is Required for Pollen Wall Development

“…Knockout of both AtSEC24B and AtSEC24C leads to defective gametophyte development (Tanaka et al, 2013). More recently, AtSAR1A and AtSEC23A were shown to interact as a pair, which is essential for protein ER export in Arabidopsis (Zeng et al, 2015). However, the function of other COPII proteins in Arabidopsis has yet to be determined.…”

MONENSIN SENSITIVITY1 (MON1)/CALCIUM CAFFEINE ZINC SENSITIVITY1 (CCZ1)-Mediated Rab7 Activation Regulates Tapetal Programmed Cell Death and Pollen Development

“…Maintenance of Arabidopsis suspension-cultured cells and transient expression methods were described previously (Miao and Jiang, 2007;Woo et al, 2015;Zeng et al, 2015;Shen et al, 2016;. The general procedures for transient gene expression analysis in leaf protoplast were performed essentially as described previously (Yoo et al, 2007).…”