Interplay between the Ubiquitin Proteasome System and Ubiquitin-Mediated Autophagy in Plants

Abstract

All eukaryotes rely on the ubiquitin-proteasome system (UPS) and autophagy to control the abundance of key regulatory proteins and maintain a healthy intracellular environment. In the UPS, damaged or superfluous proteins are ubiquitinated and degraded in the proteasome, mediated by three types of ubiquitin enzymes: E1s (ubiquitin activating enzymes), E2s (ubiquitin conjugating enzymes), and E3s (ubiquitin protein ligases). Conversely, in autophagy, a vesicular autophagosome is formed that transfers damaged proteins and organelles to the vacuole, mediated by a series of ATGs (autophagy related genes). Despite the use of two completely different componential systems, the UPS and autophagy are closely interconnected and mutually regulated. During autophagy, ATG8 proteins, which are autophagosome markers, decorate the autophagosome membrane similarly to ubiquitination of damaged proteins. Ubiquitin is also involved in many selective autophagy processes and is thus a common factor of the UPS and autophagy. Additionally, the components of the UPS, such as the 26S proteasome, can be degraded via autophagy, and conversely, ATGs can be degraded by the UPS, indicating cross regulation between the two pathways. The UPS and autophagy cooperate and jointly regulate homeostasis of cellular components during plant development and stress response.

Modulation of Abiotic Stress Responses in Rice by E3-Ubiquitin Ligases: A Promising Way to Develop Stress-Tolerant Crops

“…The different types of polyubiquitin chains generate a ubiquitin code that increases the functional plasticity of this system beyond the regulation of protein degradation through the UPS. Among those, the K63-linked chains are implicated in the degradation of proteins and cellular compartments through endocytosis and selective autophagy ( Clague and Urbé, 2010 ; Romero-Barrios and Vert, 2018 ; Su et al, 2020 ).…”

Control of ABA Signaling and Crosstalk With Other Hormones by Selective Degradation of Pathway Components

“…Thus, autophagy represents a major mechanism in plants for degrading macromolecular ubiquitinated protein aggregates as a response to stressors [3,4]. There is growing evidence that these two degradation systems are interconnected and form an integrated quality control network in response to general cellular stress [5]. Many reviews summarize the significance of ubiquitination in plant stress responses [6][7][8].…”

Special Issue on “Ubiquitin and Autophagy”

“…The “Ubiquitin and Autophagy” Special Issue features 13 papers: seven research articles [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ] and six reviews [ 8 , 9 , 10 , 11 , 12 , 13 ]. All of them are at the intersection of ubiquitin-related processes and autophagy, including the roles of: (1) ATG and UBL proteins in the UPS and autophagy [ 2 , 3 ], (2) ubiquitin-binding autophagic receptor, p62, in autophagy signaling [ 4 ], (3) LC3-interacting region (LIR) of connexins in binding to UBL proteins [ 6 ], (4) proteasomal deubiquitinating enzyme, PSMD14, in autophagy [ 7 ], (5) sorting nexins in the UPS, autophagy and endocytosis [ 8 ], (6) ubiquitin and UBL proteins in selective autophagy [ 9 ], as well as (7) structures and interactions of the UBL proteins of Atg8-family [ 13 ].…”

“…In addition to the studies on ubiquitin and autophagy in cell culture, several groups used model organisms, such as laboratory mice [ 1 , 5 ], nematode Caenorhabditis elegans [ 2 ], and social amoeba Dictyostelium discoideum [ 3 ]. Besides, the review article of Ma and colleagues discusses the interplay between the UPS and autophagy in plants [ 10 ]. Although most of the studies explored the fundamental molecular and cellular mechanisms, some of them have interesting implications for human diseases, such as cancer [ 4 ] and leukodystrophy [ 5 ].…”