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.

The potato (Solanum tuberosum L.), one of the most important food crops worldwide, is sensitive to environmental stresses. Sensor–responder complexes comprising calcineurin B-like (CBL) proteins and CBL-interacting protein kinases (CIPKs) not only modulate plant growth and development but also mediate numerous stress responses. Here, using a Hidden Markov Model and BLAST searches, 27 CIPK genes were identified in potato and divided into five groups by phylogenetic analysis and into two clades (intron-poor and intron-rich) by gene structure analysis. Quantitative reverse-transcription PCR (qRT-PCR) assays revealed that StCIPK genes play important roles in plant growth, development and abiotic stress tolerance. Up-regulated expression of StCIPK10 was significantly induced by drought, PEG6000 and ABA. StCIPK10 enhances both the ability of potato to scavenge reactive oxygen species and the content of corresponding osmoregulation substances, thereby strengthening tolerance to drought and osmotic stress. StCIPK10 is located at the intersection between the abscisic acid and abiotic stress signaling pathways, which control both root growth and stomatal closure in potato. In addition, StCIPK10 interacts with StCBL1, StCBL4, StCBL6, StCBL7, StCBL8, StCBL11 and StCBL12, and is specifically recruited to the plasma membrane by StCBL11.