Conserved and Unique Roles of Chaperone-Dependent E3 Ubiquitin Ligase CHIP in Plants

Abstract

Protein quality control (PQC) is essential for maintaining cellular homeostasis by reducing protein misfolding and aggregation. Major PQC mechanisms include protein refolding assisted by molecular chaperones and the degradation of misfolded and aggregated proteins using the proteasome and autophagy. A C-terminus of heat shock protein (Hsp) 70-interacting protein [carboxy-terminal Hsp70-interacting protein (CHIP)] is a chaperone-dependent and U-box-containing E3 ligase. CHIP is a key molecule in PQC by recognizing misfolded proteins through its interacting chaperones and targeting their degradation. CHIP also ubiquitinates native proteins and plays a regulatory role in other cellular processes, including signaling, development, DNA repair, immunity, and aging in metazoans. As a highly conserved ubiquitin ligase, plant CHIP plays an important role in response to a broad spectrum of biotic and abiotic stresses. CHIP protects chloroplasts by coordinating chloroplast PQC both outside and inside the important photosynthetic organelle of plant cells. CHIP also modulates the activity of protein phosphatase 2A (PP2A), a crucial component in a network of plant signaling, including abscisic acid (ABA) signaling. In this review, we discuss the structure, cofactors, activities, and biological function of CHIP with an emphasis on both its conserved and unique roles in PQC, stress responses, and signaling in plants.

Plant E3 Ligases and Their Role in Abiotic Stress Response

“…These E3 ligases also function as monomeric E3s and encompass less than 100 members in plants [ 54 , 55 , 56 , 57 ]. They function widely in abiotic and biotic stress responses, but have also been described, for example, in apical meristem maintenance or phytohormone signaling [ 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 ].…”

Roles of E3 Ubiquitin Ligases in Plant Responses to Abiotic Stresses

“…OsHTAS can interact with APX and 26S proteasome, thereby effectively regulating the accumulation of H 2 O 2 and functions in the leaves to enhance heat tolerance, e.g., through modulating H 2 O 2 -induced stomatal closure [127]. E3 ubiquitin ligases tend to recognize misfolded proteins with the assistance of HSPs [128], and the presence of chaperones in OsHTAS complexes is not clear. Additionally, the complete sets of OsHTAS substrates in the nucleus and the cytoplasm, and in stomatal guard cells, need to be characterized using proteomics tools in the future.…”

Chloroplasts Protein Quality Control and Turnover: A Multitude of Mechanisms

“…In metazoans, CHIP has been extensively investigated for its critical role in protein quality control. Like their counterparts in metazoans, plant CHIP contains an N-terminal tetratricopeptide repeat (TRP) and a C-terminal U-box domain [ 57 , 58 ]. The CHIP TRP domain binds directly to the conserved EEVD motifs at the C-terminus of heat shock cognates (Hsc)/Hsp70 and Hsp90 [ 59 , 60 ].…”