PIN-mediated auxin transport is crucial for light-regulated plant organogenesis; however, how light modulates PIN localization remains elusive. Cotton (Gossypium hirsutum), a key textile crop, requires ample sunlight for optimal growth and fiber development. Yet, the mechanism underlying light-regulated fiber development is obscure. Our research shows that light promotes fiber initiation and elongation through inhibiting ubiquitylation degradation of GhPIN3a and subsequently enhancing GhPIN3a plasma-membrane localization. In fiber cells, where GhPIN3a undergoes preferential ubiquitylation, GhCOP1 was identified to control ubiquitylation degradation of GhPIN3a in response to light. Dark-stabilized GhCOP1 targets GhUCH3, which interacts with GhPIN3a to balance its stability through deubiquitylation. This regulatory cascade converts light signals into developmental cues in cotton fibers. Intriguingly, while GhCOP1 promotes GhUCH3 degradation via the ubiquitin–proteasome system (UPS), GhUCH3 modulates GhPIN3a proteolysis through both the UPS and the vacuolar degradation pathway. Our findings reveal a light-regulated GhPIN3a stability mechanism through the GhCOP1–GhUCH3 module, consequently influencing cotton fiber development.

Seed germination is a crucial phase where a plant embryo transitions from dormancy to active growth, emerging as a seedling. This intricate process is highly susceptible to environmental cues, particularly abiotic stress factors including drought, salinity, and temperature extremes, which can profoundly influence both germination success and subsequent plant development. Among the various cellular components that modulate plant responses to these stresses, Rho of Plants (ROP) emerges as a pivotal regulator. Under abiotic stress, ROP signaling components integrate with the core abscisic acid (ABA) signaling pathway by regulating gene transcription and protein stability, modulating subcellular localization, converting protein activity, and engaging in competitive interactions. This review summarizes recent findings on roles of ROP signaling in regulating plant adaptive responses to abiotic stress, whilst explores potential involvement of ROPs in seed germination. This review summarizes the effects of ROP proteins and their effectors, such as GEF, on the seed germination process. It preliminarily elucidates the crosstalk mechanisms between these proteins and the ABA signaling pathway, thereby gaining a deeper understanding of the role of ROP signaling in regulating plant adaptive responses to abiotic stresses.