Abstract
Owing to a sessile lifestyle in nature, plants are routinely faced with diverse hostile environments such as various abiotic and biotic stresses, which lead to accumulation of free radicals in cells, cell damage, protein denaturation, etc., causing adverse effects to cells. During the evolution process, plants formed defense systems composed of numerous complex gene regulatory networks and signal transduction pathways to regulate and maintain the cell homeostasis. Among them, ubiquitin-proteasome pathway (UPP) is the most versatile cellular signal system as well as a powerful mechanism for regulating many aspects of the cell physiology because it removes most of the abnormal and short-lived peptides and proteins. In this system, the ubiquitin-conjugating enzyme (E2) plays a critical role in transporting ubiquitin from the ubiquitin-activating enzyme (E1) to the ubiquitin-ligase enzyme (E3) and substrate. Nevertheless, the comprehensive study regarding the role of E2 enzymes in plants remains unexplored. In this review, the ubiquitination process and the regulatory role that E2 enzymes play in plants are primarily discussed, with the focus particularly put on E2′s regulation of biological functions of the cell.
Highlights
Researchers have successfully extracted a small molecular protein from reticulocytes, and this protein is a key factor in ATP-dependent substrate proteolysis and is universally present in many organisms [1,2,3,4]
The nonproteolytic functions and mechanisms of most key enzymes which are core components of the ubiquitin-proteasome system (UPS) (Ubiquitin-proteasome system) are still unclear, especially E3s and E2s (37 E2s are encoded in A. thaliana genome) [8,21]
This study suggests that Fni3/Sl-Ubc13-2 and Suv positively regulate plant immunity [128]
Summary
Researchers have successfully extracted a small molecular protein (initially called APF-1 and later renamed as “Ubiquitin”) from reticulocytes, and this protein is a key factor in ATP-dependent substrate proteolysis and is universally present in many organisms [1,2,3,4] Based on these experiments and later research findings, the Nobel Prize in Chemistry was awarded to Aaron Ciechanover, Avram Hershko and Irwin Rose in 2004, for their outstanding contributions to the discovery of ubiquitin-mediated protein degradation [5]. The nonproteolytic functions and mechanisms of most key enzymes (over 1600 loci in Arabidopsis thaliana genome) which are core components of the UPS (Ubiquitin-proteasome system) are still unclear, especially E3s (more than 1400 potential E3s are encoded in A. thaliana genome) and E2s (37 E2s are encoded in A. thaliana genome) [8,21] It will be an important task for future research to uncover the role of these enzymes
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