The Scaffolding Protein RACK1: A Platform for Diverse Functions in the Plant Kingdom

The receptor for activated C kinase 1 (RACK1) is one of the well-known WD-repeat containing proteins and can interact as a scaffolding protein with many different signaling proteins from distinct signal transduction pathways. Accordingly, it acts as a platform for diverse functions in both prokaryotes and eukaryotes. In metazoan and yeast, RACK1 is known to be involved in regulating development, circadian rhythm, cell migration, diseases, etc. However, the roles of RACK1 are largely unclear in plant kingdom. Nevertheless, great progresses have been made in recent years on the roles of plant RACK1. Plant RACK1 is highly similar to mammalian RACK1 at the amino acid level and in structure, although some differences in amino acid sequence of RACK1 proteins have been found between monocots and dicots as well as between human and plants, which can explain, at least in part, the differences of RACK1 functions. Several recent studies have shown that plant RACK1 is involved in the responses to plant hormones, abiotic/biotic stresses, plant growth and development, etc. And the molecular mechanisms of RACK1 functions have also been explored, although the gap is still obvious between plants and metazoan. However, a deep understanding of the molecular mechanisms of RACK1 functions is expected as the progress in screening and identification of more and more RACK1-interacting signaling molecules.