The Protein Quality Control of Plant Receptor-Like Kinases in the Endoplasmic Reticulum

Plant receptor-like kinases (RLKs) play important roles in regulating plant growth and development and plant–microbe interactions. Like other eukaryotic membrane and secretory proteins, RLKs are cotranslationally inserted into the endoplasmic reticulum (ER) for chaperone-assisted folding to attain their native structures before reaching the plasma membrane to perceive developmental or environmental signals. The ER also houses complex quality control (ERQC) systems that retain incompletely folded proteins for additional folding attempts but eliminate terminally misfolded proteins by ER-associated degradation (ERAD). However, little is known about how the protein folding and ERQC/ERAD events are executed in the plant ER. Recent genetic and biochemical approaches designed to identify regulators of RLK signaling fortuitously discovered various components of the plant ERQC/ERAD systems. These studies have not only dramatically enhanced our understanding of the plant ERQC/ERAD mechanisms that regulate the cell surface expression of RLKs, but have also provided outstanding tools that could identify additional ERQC/ERAD components and uncover novel RLKs involved in plant environment communications.