COPII Paralogs in Plants: Functional Redundancy or Diversity?

In eukaryotes, the best-described mechanism of endoplasmic reticulum (ER) export is mediated by coat protein complex II (COPII) vesicles, which comprise five conserved cytosolic components [secretion-associated, Ras-related protein 1 (Sar1), Sec23–24, and Sec13–31]. In higher organisms, multiple paralogs of COPII components are created due to gene duplication. However, the functional diversity of plant COPII subunit isoforms remains largely elusive. Here we summarize and discuss the latest findings derived from studies of various arabidopsis COPII subunit isoforms and their functional diversity. We also put forward testable hypotheses on distinct populations of COPII vesicles performing unique functions in ER export in developmental and stress-related pathways in plants.

TrendsCoat protein complex II (COPII) comprising five cytosolic components (Sar1, Sec23–24, and Sec13–31) is specialized in mediating protein export from the endoplasmic reticulum (ER). These highly conserved COPII components are essential subunits for the formation of COPII vesicles in eukaryotes.Twenty-one COPII subunit paralogs have been identified in arabidopsis (Arabidopsis thaliana), largely outnumbering those in other organisms.Recent studies suggest the functional diversity of various arabidopsis COPII subunit paralogs, while deficiencies in certain paralogs cause distinct effects in protein export from the ER and developmental defects in plants.A plant-unique mechanism in COPII-mediated protein export was recently demonstrated by the specific preferential pairing between AtSar1a and AtSec23a in arabidopsis.Microarray data have revealed distinct expression profiles of arabidopsis COPII subunit paralogs during various developmental stages and stress conditions, indicating their functional diversity in plants.