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Plant hormones are essential small molecules that regulate plant growth, development, and systemic responses to environmental stimuli. These processes are mediated by complex signaling networks involving structurally diverse receptors, regulatory proteins, and dynamic protein–protein interactions. Advances in structural and functional biology over the past two decades have revealed how hormone receptors recognize their ligands and how they mediate responses from perception to signaling through transduction pathways and feedback regulation. In this review, we summarize the current knowledge of plant hormone receptors with experimentally determined structures and highlight their central roles in shaping plant biology. Finally, we discuss outstanding questions in the field and how emerging computational tools may help address these gaps. 

SUMMARY The ubiquitin system plays a central role in regulating plant growth, development, and immune responses. Within this system, E3 ubiquitin ligases act as key specificity factors that direct the modification and degradation of immune receptors, transcription factors, kinases, and hormone regulators. Recent advances reveal how diverse E3 ligase families, including Cullin–RING ligases (CRLs), RING‐type, U‐box, and RBR‐type ligases, modulate both pattern‐triggered and effector‐triggered immunity. This review integrates new mechanistic and structural insights that clarify how E3s recognize substrates, assemble with E2 enzymes, and interface with pathogen effectors. Together, these studies uncover conserved catalytic principles and indicate pathogen‐driven diversification of ubiquitin signaling. Emerging themes include feedback regulation, E3–E3 antagonism, and crosstalk with hormone pathways that balance defense and growth. Collectively, these findings redefine the ubiquitin–proteasome system as a dynamic regulatory network integrating perception, signaling, and proteostasis during plant immunity, offering new conceptual and practical avenues for enhancing disease resistance. 

Plants utilize the ubiquitin proteasome system (UPS) to orchestrate numerous essential cellular processes, including the rapid responses required to cope with abiotic and biotic stresses. The 26S proteasome serves as the central catalytic component of the UPS that allows for the proteolytic degradation of ubiquitin-conjugated proteins in a highly specific manner. Despite the increasing number of studies employing cell-free degradation assays to dissect the pathways and target substrates of the UPS, the precise extraction methods of highly potent tissues remain unexplored. Here, we utilize a fluorogenic reporting assay using two extraction methods to survey proteasomal activity in different Arabidopsis thaliana tissues. This study provides new insights into the enrichment of activity and varied presence of proteasomes in specific plant tissues. 

Chloroplasts are ancient organelles responsible for photosynthesis and various biosynthetic functions essential to most life on Earth. Many of these functions require tightly controlled regulatory processes to maintain homeostasis at the protein level. One such regulatory mechanism is the ubiquitin-proteasome system whose fundamental role is increasingly emerging in chloroplasts. In particular, the role of E3 ubiquitin ligases as determinants in the ubiquitination and degradation of specific intra-chloroplast proteins. Here, we highlight recent advances in understanding the roles of plant E3 ubiquitin ligases SP1, COP1, PUB4, CHIP, and TT3.1 as well as the ubiquitin-dependent segregase CDC48 in chloroplast function.