A correct three-dimensional structure is crucial for the physiological functions 
of a protein, yet the folding of proteins to acquire native conformation is a 
fundamentally error-prone process. Eukaryotic organisms have evolved a highly 
conserved endoplasmic reticulum-mediated protein quality control (ERQC) 
mechanism to monitor folding processes of secretory and membrane proteins, 
allowing export of only correctly folded proteins to their physiological 
destinations, retaining incompletely/mis-folded ones in the ER for additional 
folding attempts, marking and removing terminally misfolded ones via a unique 
multiple-step degradation process known as ER-associated degradation (ERAD). 
Most of our current knowledge on ERQC and ERAD came from genetic and biochemical 
investigations in yeast and mammalian cells. Recent studies in the reference 
plant Arabidopsis thaliana uncovered homologous components and similar 
mechanisms in plants for monitoring protein folding and for retaining, 
repairing, and removing misfolded proteins. These studies also revealed critical 
roles of the plant ERQC/ERAD systems in regulating important 
biochemical/physiological processes, such as abiotic stress tolerance and plant 
defense. In this review, we discuss our current understanding about the 
molecular components and biochemical mechanisms of the plant ERQC/ERAD system in 
comparison to yeast and mammalian systems.