Xinye Li

The ubiquitin-26S proteasome system provides a key mechanism for regulating protein turnover in plants and contributes to the control of diverse developmental and stress-related processes. Within this system, Skp1-Cullin1-F-box (SCF) E3 ligases rely on F-box proteins to confer substrate specificity, enabling selective and dynamic regulation of target protein stability. The large size and structural diversity of the F-box protein family in plants suggest extensive functional specialization, although many members remain poorly characterized. Here, we review recent advances in the understanding of F-box protein function, with a focus on their roles in plant development, stress adaptation, and immunity. Specifically, this review integrates findings across development, abiotic stresses, and immunity to highlight shared and diverging regulatory nodes and critically assesses the strength of substrate evidence to distinguish bona fide from putative F-box targets. We highlight how F-box proteins modulate key regulatory pathways, including phytohormone signaling, reproductive development, root architecture, and secondary metabolism, as well as responses to abiotic and biotic stresses. Emerging evidence indicates that F-box-mediated proteolysis acts as an important layer of control linking environmental signals to downstream transcriptional and physiological outputs. A better understanding of F-box protein substrates and regulatory networks is important for dissecting plant adaptive mechanisms and may provide molecular targets for future crop improvement strategies.

Autophagy is a conserved degradation pathway essential for cellular homeostasis in plants. Selective autophagy confers cargo specificity through receptors, among which NEIGHBOR OF BRCA1 GENE1 (NBR1) is one of the best-characterized. NBR1 mediates the selective turnover of ubiquitinated or stress-damaged cargoes, including protein aggregates and damaged organelles, by linking them to ATG8-decorated autophagosomes via its AIM and UBA domains. This process supports proteostasis, plant development, and adaptation to abiotic stresses, including heat, drought, chilling, salinity, and heavy metals, as well as biotic stresses from bacteria, fungi, viruses, and oomycetes. In this review, we summarize current advances in understanding NBR1 structure, evolutionary conservation, and cargo recognition mechanisms, and highlight its interplay with phytohormone signaling and the ubiquitin–proteasome system (UPS) in shaping plant growth and stress resilience.